Source Of Ore-forming Fluids Research Articles

Textural and chemical evolution of magnetite from the Paleozoic Shuanglong Fe-Cu deposit: Implications for tracing ore-forming fluids

Abstract The Aqishan-Yamansu belt in Eastern Tianshan (NW China) hosts several important Fe and Fe-Cu deposits, the origin of which is the subject of considerable debate. The coexistence of various types of ore-forming fluids makes it difficult to distinguish the genesis of the Fe-Cu deposits. We present detailed textural and compositional data on magnetite from the Paleozoic Shuanglong Fe-Cu deposit to constrain the formation of iron oxides and the evolution of the ore-forming fluids and thus define the genesis of the Fe-Cu ores. Based on the mineral assemblages and crosscutting relationships of veins, two mineralization stages were established, including the early Fe mineralization and late Cu mineralization stage. Three types of magnetite, i.e., platy (MA), massive (MB), and granular (MC) magnetite occur in the Fe mineralization. Backscattered electron (BSE) images identified display oscillatory zoning in an early hematite and transformational mushketovite phase (MA-I), characterized by abundant porosity and inclusions, as well as two later generations, including an early dark (MA-II, MB-I, and MC-I) and later light magnetite (MA-III, MB-II, and MC-II). The MA-I has extremely high W contents and mostly displays as micro- and invisible scheelite inclusions, which were probably caused by the W expulsion during mushketovitization. The texture and composition of magnetite suggest that the later light magnetite formed via dissolution and reprecipitation of the precursor dark magnetite, and the temperature and oxygen fugacity of fluids decreased over time. Our study also shows the MB-II magnetite and coexisting chlorite display synchronous oscillatory zoning, with the calculated temperature from 444 to 212 °C. Such variations could indicate the incursion of external low-temperature fluids with high salinity, which can dissolve the primary dark magnetite. This study provides a good example of using magnetite to trace the complex evolution and multiple sources of ore-forming fluids.

Cassiterite oxygen isotopes in magmatic-hydrothermal systems: in situ microanalysis, fractionation factor, and applications

Tin and tungsten are important metals for the industrializing society. Deciphering the origin and evolution of hydrothermal fluids responsible for their formation is critical to underpin genetic models of ore formation. Traditional approaches obtain isotopic information mainly from bulk analysis of both ore and gangue minerals, or less frequently from in situ analysis of gangue minerals, which either bear inherited complexities and uncertainties or are indirect constraints. Hence, directly obtaining isotopic information from ore minerals such as cassiterite by in situ techniques is warranted. However, this has been hampered by challenges from both analytical and applicational aspects. In this study, we first demonstrate a lack of crystallographic orientation effects during cassiterite ion microprobe oxygen isotope analysis. Along with our newly developed matrix-matched reference material, the Yongde-Cst, which has a recommended δ18O value of 1.36 ± 0.16‰ (VSMOW) as defined by gas source isotope ratio mass spectrometry, in situ oxygen isotope analysis of cassiterite now is possible. We further refine the oxygen isotope fractionation (1000 ln α) for quartz-cassiterite by first-principles calculations, which is given by the equation of 1.259 × 106/T2 + 8.15 × 103/T − 4.72 (T is temperature in Kelvin). The 1000 ln α for quartz-cassiterite has a sensitive response to temperature, and makes cassiterite-quartz an excellent mineral pair in oxygen isotope thermometry, as described by the equation of T (℃) = 2427 × (δ18Oqtz − δ18Ocst)−0.4326 − 492.4. Using the well-established 1000 ln α of quartz-water, 1000 ln α of cassiterite-water is derived as 2.941 × 106/T2 − 11.45 × 103/T + 4.72 (T in Kelvin), which shows a weak response to temperature. This makes cassiterite an ideal mineral from which to derive δ18O of fluids as robust temperature estimates are no longer a prerequisite. We have applied oxygen isotope analysis to cassiterite samples from six Sn(-W) deposits in China. The results show considerable variability in δ18O values both within a single deposit and among studied deposits. Combining the δ18O of cassiterite samples and the equilibrium oxygen isotope fractionation, we find that the δ18O values of ore-forming fluids show a strong magmatic affinity with variable but mostly no to low degree involvements (~0-10%) of meteoric water, hence our results invite a reassessment on the extent and role of meteoric water in Sn-W mineralization. This study demonstrates that in situ oxygen isotope analysis of cassiterite is a promising tool to refine sources of ore-forming fluids, and to decode hydrothermal dynamics controlling tin and tungsten mineralization.

Texture, trace elements, sulfur and He-Ar isotopes in pyrite: Implication for ore-forming processes and fluid source of the Guoluolongwa gold deposit, East Kunlun metallogenic belt

The Gouli goldfield is the most important gold producers of the East Kunlun metallogenic belt. Gold mineralization in this region is enigmatic, primarily because of uncertainties as to the mineralization processes, and the nature and sources of ore-forming fluids. Here, we investigate the ore-forming fluids and processes through a comprehensive study of the texture and geochemistry (LA-(MC)-ICPMS trace element analysis, mapping, S isotopes, and He-Ar isotopes) of pyrite from the Guoluolongwa gold deposit, the largest deposit in the Gouli goldfield. Four types of pyrite with distinct textures, trace element contents and sulfur isotopes were identified, and provide evidence for a multi-stage hydrothermal fluid evolution. The sedimentary-diagenetic Py0, representing the pre-ore stage, is characterized by high contents of Co and Ni, and negative δ34S values (−11.6‰ to −4.0‰), which are notably different from the subsequent hydrothermal Py1 to Py3. Hydrothermal Py1, comprising subtypes Py1a and Py1b, was deposited in pyrite-quartz veins during stage I. The Py1a subtype shows characteristic Co-Ni-As oscillatory zoning that replaced Py0 via dissolution-reprecipitation, and hence inherited high concentrations of Co and Ni from Py0. In contrast, the Py1b subtype was devoid of Py0 influence and represented the initial ore-forming fluid with low concentrations of Co and Ni, moderate Cu, Pb, Zn, Sb, and Bi, but high As, Au, and Ag. The next stage, Py2, formed in the quartz-pyrite veins during stage II and showed clear textural and compositional contrasts to Py1. Specifically, Py2 has elevated Cu, Pb, Zn, Ag, and Bi contents and somewhat lower δ34S values (+1.5‰ to +3.2‰) compared to Py1 (+1.6‰ to +5.6‰). In addition, Py2 shows irregular compositional zones, which we attribute to fluid phase separation caused by pressure fluctuation. Abundant Py2 precipitation triggered native gold deposition due to desulfidation of the ore-forming fluid. The next stage, Py3 in polymetallic sulfides-calcite-quartz veins at stage III, implies a new pulse of Cu-Pb-Zn-As-Au-Ag-rich and Bi-poor ore-forming fluid. This latter pyrite is characterized by inclusion-rich cores (Py3c), which contain abundant inclusions of chalcopyrite, galena, sphalerite, and native gold, and inclusion-free rims (Py3r). The cores, Py3c, likely represent abrupt destabilization of metal complexes and rapid precipitation during vigorous phase separation, whereas the euhedral Py3r rims formed under steadier physico-chemical conditions, contributing to lower δ34S values of Py3c (+0.5‰ to +3.0‰) than Py3r (+1.9‰ to +3.6‰). Noble gas isotopes of Py1-Py3 have crust-dominated 3He/4He (0.04–0.4 Ra) and 40Ar/36Ar (623–2081), mixed with minor mantle components. Sulfur isotopes and low Co and Ni contents of hydrothermal pyrite, and He-Ar isotopes of fluid inclusions in pyrite, are consistent with a model in which multiple pulses of ore-forming fluids were exsolved during sequential episodes of primarily crustal-derived felsic magmatism with lesser mantle influences. This model is also supported by previous H-O isotope analyses, as well as widespread granitoid magmatism in the eastern Central East Kunlun Belt.

Occurrence and remobilization of gold in the Dayingezhuang deposit in Jiaodong, North China Craton: Evidence from textural and geochemical features of pyrite

The Dayingezhuang gold deposit in the Jiaodong district, eastern margin of the North China Craton is hosted in Mesozoic granitic rocks and consists of quartz-sulfide veins/veinlets and sulfide disseminations in alteration envelopes. Previous studies mainly focused on the geochronology, sources of ore-forming fluids and metals to investigate the ore genesis. However, enrichment mechanism of Au and other associated trace metals remain unclear. In this study, we present detailed textures and in-situ LA-ICP-MS trace-element compositions of different generations of pyrite, as well as EMP analysis of Au-bearing minerals to discuss the occurrence and enrichment mechanism of Au at this deposit.Three generations of pyrite (Py1, Py2 and Py3) formed during three hydrothermal ore stages (I, II, and III) at Dayingezhuang. Py1 occurs as disseminations in sericitic alteration assemblages and is characterized by low Au (mean 0.15 ppm), Ag, As and Te contents. The time-resolved depth-concentration profiles indicate that Au in Py1 mainly occurs as nanoparticles and/or micron-sized inclusions. Py2 can be further divided into the early undeformed Py2a and later Py2b, which is the product of deformed Py2a with different degrees of brittle to plastic deformation and recrystallization. Py2a in pyrite-siderite-quartz veins is relatively enriched in invisible Au (mean 0.41 ppm), Ag, As, and Te compared to Py1, and contains numerous micron-sized Au inclusions. In contrast, Py2b contains lesser invisible Au (0.21 ppm) and host abundant gold minerals along the grain boundaries and microfractures. Py3 in polymetallic sulfide veins has little Au. As a whole, Au in pyrite is positively correlated with Ag and Te, which is consistent with the results of EMP analysis showing the occurrence of Au as electrum, native gold and minor petzite in pyrite. Such evidences show that the deformation and recrystallization of auriferous Py2a potentially caused local remobilization of Au (mainly as micron-sized inclusion Au) via solid-state ductile flow and subsequent reconcentration of Au in microfractures of Py2b. The pyrite deformation and Au remobilization events were suggested to be related to the continuous reactivation of the regional Zhaoping Fault contemporaneous with gold mineralization. Our study highlights the importance of remobilization and reconcentration of Au triggered by syn-ore tectonic activities at Dayingezhuang and possibly other Au deposits in the Jiaodong district.

Ore formation of the Dayakou emerald deposit (Southwest China) constrained by chemical and boron isotopic composition of tourmaline

The Cretaceous Dayakou emerald deposit (southwest China) hosted in the Neoproterozoic schists and granofels is a magmatic-hydrothermal ore system. In this paper, we present the petrological and geochemical study of tourmaline from the Dayakou deposit, aiming to constrain the source of ore-forming fluid and emerald genesis. Two types of tourmaline, namely type-I formed in emerald-bearing quartz veins and type-II in non-mineralized quartz veins, are distinguished and analyzed in situ for their chemical and boron isotopic compositions. All tourmalines are close to the dravite endmember and belong to the alkali group. The type-I tourmaline has a higher Fe/(Fe + Mg) ratio (0.28–0.47) with Li enrichment (21–227 ppm). The type-II tourmaline, however, shows a lower Fe/(Fe + Mg) ratio (0.14–0.34) with relatively higher Co (2–3 ppm) and REEs (2–21 ppm) content. Boron isotopic composition in tourmaline (δ11B = −15.8‰ to −10.4‰) is closed to the average boron composition of continental crust. The boron isotope variations could be the result of rapid precipitation of tourmaline from a magmatic-hydrothermal fluid or the mixing with a metamorphic fluid. Based on the chemical composition and enrichment in granitophile elements (e.g., Li, Be, Sn) and transition metals (e.g., Ti, V, Cr) in tourmaline, we propose that the Dayakou deposit is dominantly controlled by the fluid-rock interaction between the metamorphic basement and possibly reduced magmatic-hydrothermal fluids. Beryllium is transported as fluoride complex in fluids. Hydrothermal fluids continuously interacted with surrounding rocks to extract Cr, V, and Ca into fluids, resulting in extensive crystallization of fluorine minerals (e.g., fluorite, fluorapatite, etc.) and subsequent destabilization of Be-F complexes. The large amounts of Be, Cr and V enriched in the fluid then combine to form emeralds. The Li, Co, and REEs contents of tourmaline can be used as the exploration indicator to target emerald mineralization in this region.

Texture, geochemistry, and geochronology of titanite and pyrite: Fingerprint of magmatic-hydrothermal fertile fluids in the Jiaodong Au province

AbstractThe Au mineralization in the giant Jiaodong Au province is enigmatic and difficult to fit current classic mineralization models, primarily because of uncertainties as to the sources of ore-forming fluids and metals. The ca. 120 Ma Au mineralization has been previously proposed to have occurred during a magmatic lull, which would negate a magmatic-hydrothermal genetic model. However, recent drilling has revealed a buried mineralized monzonite equivalent in age to the Au mineralization in the Linglong goldfield. Here, we present comprehensive textural, geochemical [LA-(MC)-ICP-MS trace element, Nd and S isotopes] and geochronological (LA-ICP-MS U-Pb dating) analyses of titanite and pyrite from this previously unrecognized monzonite. Three types of titanite were distinguished, including magmatic Ttn1 and hydrothermal Ttn2 and Ttn3, which show indistinguishable U-Pb ages (120.7 ± 3.1 and 120.9 ± 2.6 Ma), REE patterns and Nd isotopes [εNd(t) = –14.7 to –12.9], implying that hydrothermal fluids were directly exsolved from the monzonitic magma, contemporaneous with the large-scale Au mineralization at ca. 120 Ma. The Nd isotopes of titanite potentially indicate a lower crustal source mixed with mantle materials for the monzonite. Four types of pyrite were analyzed, including magmatic Py1 from fresh biotite monzonite, hydrothermal Py2 from altered biotite monzonite, hydrothermal Py3 from quartz-pyrite veins with a monazite U-Pb age of 118.2 ± 4.6 Ma, and magmatic Py4 from mafic enclaves of the Gushan granite at ca.120 Ma. The δ34S values of magmatic Py1 and Py4 (+1.9 to +6.3‰, and +5.0 to +6.4‰, respectively) and hydrothermal Py2 and Py3 (+6.4 to +9.5‰ and +6.5 to +7.6‰, respectively) are consistent with sulfur isotopic fractionation between melt and fluid. Hydrothermal Py2 and Py3 also have higher Co, As, Ag, Sb, and Bi contents and submicrometer gold inclusions, implying that the magmatic-hydrothermal fluids were fertile for mineralization. This study highlights the importance of monzonite magmatism and exsolved fertile fluids in regional Au mineralization. Hydrous magmas at ca.120 Ma probably extracted Au efficiently from the lower crustal-mantle sources and released auriferous fluids at the late magmatic stage, leading to the formation of Au deposits in the Jiaodong province.

Origin of ore-forming fluids of Tokuzbay gold deposit in the South Altai, northwest China: Constraints from Sr–Nd–Pb isotopes

• A low I Sr (t) fluid system is required for formation of Tokuzbay gold deposit. • Pb isotopes of sulfides are similar with the ore hosting Altai Formation. • The gold mineralization may have originated from the metamorphic dehydration of sediments of Altai Formation. Orogenic gold deposits are the most important gold resource in the world. It is controversial whether their ore-forming fluids were sourced from metamorphic dehydration of the crust or the mantle. The Tokuzbay gold deposit is a typical orogenic-type gold deposit in the Central Asian Orogenic Belt , providing a case for discussing the source of ore-forming fluids. The auriferous quartz veins are fault-controlled and occur mainly in metamorphic sediments of Devonian Altai Formation and minor in diorite dikes, forming three ore types, i.e., quartz vein, altered metamorphic sediments and altered diorite dikes. We studied the Sr–Nd–Pb isotope characteristics of the ore sulfides, and magmatic and metamorphic rocks from the Tokuzbay gold deposit, and thereby discuss the source of the ore-forming fluids. The 87 Sr/ 86 Sr ratios of meta -sediment hosted ores scatter between 0.709474 and 0.715238, and I Sr (292 Ma) values range from 0.706570 to 0.714045. The diorite dikes hosted ores show more restricted 87 Sr/ 86 Sr ratios ranging from 0.706963 to 0.711519, and I Sr (292 Ma) values ranging from 0.706777 to 0.710612. The wall rocks of the Altai Formation have I Sr (292 Ma) values of 0.711778 and 0.714409, which are higher than ore sulfides. This indicates that the I Sr (292 Ma) values of initial ore-forming fluids that interacted with the Altai Formation are no higher than 0.706777, which is the lowest I Sr (292 Ma) value for disseminated ores. The calculated ( 143 Nd/ 144 Nd) i ratios and ε Nd (292 Ma) values for meta -sediment hosted ores range from 0.511882 to 0.512464, and −7.4 to 4.0, respectively. The calculated ( 143 Nd/ 144 Nd) i ratios and ε Nd (292 Ma) values for diorite dike hosted ores vary from 0.512293 to 0.512562, and from 0.6 to 5.9, respectively. The meta -sediments of Altai Formation show ε Nd (292 Ma) values ranging from −6.8 to −4.4 with an average of −5.8, which are lower than those of ore sulfides. This indicates that the ε Nd (292 Ma) values for the fluids that interacted with the wall rocks cannot be lower than 4.5, which is the average value for disseminated ores. The calculated ( 208 Pb/ 204 Pb) i , ( 207 Pb/ 204 Pb) i , and ( 206 Pb/ 204 Pb) i values of ore sulfides are 37.796–38.989, 15.512–15.707, 17.988–18.100, respectively. The wall rocks of the Altai Formation show relatively higher ( 206 Pb/ 204 Pb) i ratios, indicating that the ore-forming fluid that interacted with the Altai Formation are not higher than 17.988, which is the lowest values of sulfides from disseminated ores. Based on the Sr–Nd–Pb isotope data, we suggest the possible ore-forming fluids should have lower I Sr (292 Ma) values, higher ε Nd (292 Ma) values, and lower ( 206 Pb/ 204 Pb) i values compared to the those of ore sulfides and were possibly sourced from a source compositionally similar to the diorite dikes in addition to wall rocks of Altai Formation. Combining with the regional metamorphism and tectonic evolution , we suggest that the ore fluids have originated from the metamorphic dehydration of sediments of Altai Formation in the South Altai during the collision between Altai Orogen and Junggar Plate.

Microthermometry and noble gas isotope analysis of magmatic fluid inclusions in the Kerman porphyry Cu deposits, Iran: constraints on the source of ore-forming fluids

This paper reports microthermometric and noble gas isotope data for fluid inclusion assemblages (FIAs) with evidence of phase separation, i.e. coexisting vapor-rich and halite-saturated inclusions, hosted in the early-formed quartz stockwork veins and post-magmatic quartz eye crystals in two economic porphyry Cu deposits (PCDs; Sar Cheshmeh and Miduk) and two sub-economic prospects (Sar Kuh and Abdar) from the Kerman porphyry copper belt (KPCB), Iran. The multiphase halite-saturated inclusions (i.e., Type I) in all studied PCDs and prospects had the highest homogenization temperature (Th = 525–594 °C) and salinities (63–73 wt% NaClequiv), whereas vapor-rich inclusions (Type II) had lower Th (362–460 °C). Fluid inclusion data show that like economic PCDs, the sub-economic prospects were formed in a fertile hydrothermal system and benefited from a mineralizing fluid, which evolved from a primary hot (mostly > 400 °C), metal-rich and oxidized fluid (as evidenced by the presence of opaque- and hematite-bearing fluid inclusions) of unknown salinity, which underwent a phase separation process to form both brine and vapor phases in the early stage of mineralization. The helium abundance and its isotopic composition document a mantle-derived magmatic source for the primary ore fluid in the formation of the studied PCDs and prospects (3He/4He ratios ranging from 0.46 to 2.8 Ra, corresponding to a mantle He contribution in ore fluids between ~ 7 and 45%). However, subsequent hydrothermal processes, i.e., vapor–brine phase separation, fluid-rock interaction with crustal rocks, and mixing with meteoric pore water containing dissolved atmospheric (e.g., Ne and Xe) and some crustal noble gases (e.g., Ar), changed the initial noble gas composition of the magmatic ore fluid to predominantly atmospheric- and crustal-like compositions. A significant proportion of mantle-derived He (up to 45%) in high-temperature (513–594 °C) and high-salinity (61.5–73 wt% NaClequiv) FIAs may indicate the existence of buried, economic, porphyry Cu mineralization in the Abdar prospect; therefore, it is suggested to be a possible target for further exploration. Comparing the He and Ar noble gas isotope composition in porphyry copper systems of different size and economic importance in this study showed that the ore-forming fluids of the outsized PCD (i.e., Sar Cheshmeh) have higher contributions of crustal-derived fluids characterized by predominantly radiogenic noble gas signatures (4He and 40Ar) than the smaller PCDs. This could have been achieved by a prolonged hydrothermal circulation in a large volume of crustal rocks containing radiogenic noble gases under a long-lived heat regime resulting from a deeply emplaced and slowly cooled composite intrusive body.

Mineralogical Characteristics and in-situ Sulfur Isotopic Analysis of Gold-Bearing Sulfides from the Qilishan Gold Deposit in the Jiaodong Peninsula, China

Large-scale gold mineralization during the Early Cretaceous is identified in the Jiaodong Peninsula of China. Sources of ore-forming fluids remain debated. We study the Qilishan gold deposit in the northwestern Jiaodong Peninsula with detailed mineralogical observation and in-situ sulfur isotope analyses, in order to reveal the gold occurrence and the origin of ore-forming fluids. The Qilishan gold deposit is mainly clastic altered rock-type in mineralization, and ore minerals are visible native gold, electrum, pyrite, chalcopyrite and galena, gangue minerals as quartz, sericite and calcite. The gold occurrence includes inclusion and intergranular types, formed within pyrites and chalcopyrites and along their fissures. In-situ sulfur isotope analysis of gold-bearing sulfides suggests that the Qilishan deposit is enriched in heavy sulfur, with δ34S values mainly from +8.0‰ to +12.0‰. δ34S values increase gradually with the fluid evolution from the early to late stages, which is interpreted to be related to the loss of sulfur via sulfide precipitation. The crystallization of sulfides from hydrothermal fluids may have triggered the instability of Au(HS)2, and finally led to gold precipitation. Combined with sulfur isotope compositions of other gold deposits (n=43) and wall-rocks in the Jiaodong Peninsula, it is proposed that the ore-forming fluids were probably not directly originated from metamorphic wall-rocks (e.g., Jiaodong Group). Moreover, the relatively long time interval rules out the possibility that the gold mineralization (ca. 120 Ma) was associated with granitic magma activities (mostly 160–150 Ma). Possible ore genesis scenario is that, long-term subduction of slabs (e.g., the Paleo-Pacific) with gold-enriched pyritic materials and crustal sedimentary rocks resulted in both high Au contents and positive δ34S values of sulfur in the lithospheric mantle below the North China Craton. Subsequently, devolatilization of the metasomatized mantle produced auriferous fluids that migrated upward along translithospheric fault systems, and gold finally precipitated in favorable structural positions, generating the world-class Jiaodong deposits in the Early Cretaceous.

Contrast between metamorphic and ore-forming fluids in the Ailaoshan belt, southeastern Tibet: New constraints on ore-fluids source for its orogenic gold deposits

The source of ore-forming fluids for orogenic gold deposits is still disputed with models ranging from derivation from metamorphism of continental crust to derivation from metasomatized mantle lithosphere. This dispute is addressed by this study of the Ailaoshan orogenic gold belt, southeastern Tibet, whose evolution involved intense metamorphism on the eastern side of the Ailaoshan shear zone. Both the regional metamorphic barren quartz veins and gold-related quartz veins in this belt are genetically related to movement on the Ailaoshan shear zone and thus formed over the same limited age span. Microthermometry, fluid compositions and stable isotope analyses conducted on both metamorphic fluids extracted from regional metamorphic quartz veins and ore-forming fluids collected from auriferous quartz veins at Zhenyuan and Jinchang gold deposits reveal significant differences. These include: (1) regional metamorphic quartz veins contain three types of fluid inclusions, including CO2-rich, aqueous-CO2 and aqueous types. The CO2-bearing inclusion types are more abundant than those in auriferous quartz veins; (2) those fluids from barren metamorphic veins with high CO2 content (up to 45 mol%) are typified by low-medium temperature (217–418 °C), low salinity (2–8 wt% NaCl) and variable pressure (28–440 MPa), and belong to the NaCl-CO2-H2O system. In contrast, the ore-forming fluids, which exhibit lower temperature (mainly 170–270 °C), higher salinity (mainly 5–13 wt% NaCl), and lower pressure (20–282 MPa and 14–44 MPa for Zhenyuan and Jinchang, respectively), belong to the NaCl-H2O-CO2 system; (3) the metamorphic fluids contain high Ca2+ and Mg2+ in liquids and CO2, N2 and CO in gases, whereas the ore-forming fluids are enriched in K+ in liquid and H2O, CO2, CH4 in gases; (4) the pyrites from regional metamorphic quartz veins have δ34S values ranging from 2.08 to 2.86‰ (mean = 2.50‰), indicating a single sulfur source of metamorphic fluids, thus contrasting with the broad range of δ34S values of ore sulfides. These distinctions negate a genetic relationship between crustal metamorphism and gold mineralization and demonstrate that ore-fluids that deposit orogenic gold deposits, at least in the Ailaoshan belt cannot be derived or evolved from crustally-derived regional metamorphic fluids. This provides a new line of evidence for the derivation of ore-forming fluids from a sub-crustal, metasomatized mantle lithosphere source for at least some orogenic gold deposits.

Textural, compositional and isotopic characteristics of pyrite from the Zaozigou gold deposit in West Qinling, China: Implications for gold metallogeny

The Zaozigou gold deposit (ZZGD) located within the West Qinling Orogen in China, with 142 t of Au at an average grade of 2.69 g/t, is hosted in a sequence of metasediments and altered dacitic to granodioritic rocks. The majority of gold is present as invisible gold in disseminated arsenian pyrite. Here we investigate the morphological and compositional evolution of the pyrite grains and constrain the ore-forming fluid source(s) and genetic models related to the ore-forming processes through the application of Scanning electron microscopy, electron probe microanalysis, in-situ laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and fsLA-MC-ICP-MS analyses. Based on texture and trace element concentrations, we identify five generations of pyrite (namely, Py1, Py2, Py3, Py4, and Py5). Among these, the pre-ore framboidal pyrite (Py1), which is characterized by relatively low concentrations of As, Au, Co, Ni, and Sb, has negative δ34S values of −31.07 to −20.79‰, which we correlate to bacterial reduction of marine sulfate during sedimentation and diagenesis. The auriferous Py2 and Py5, which occur as either porous aggregates or epitaxial overgrowth on earlier pristine pyrite, contain relatively high concentrations of As, Sb, Tl, and Au compared with pyrite in the other generations. Both (Py2 and Py5) display a relatively narrow range of negative δ34S values, ranging from −5.66 to −1.16‰, which are interpreted to result from a magmatic source. Gold-free Py3 and Py4 exhibit relatively variable δ34S values of −17.1 to −6.02‰, indicating that a small amount of sulfur in the sedimentary strata was added to the magmatic hydrothermal systems during fluid-rock interaction. Sulfur isotopes and LA-ICP-MS mapping of pyrite grains revealed that the gold endowment of the ZZGD is associated with multiple mineralizing events and multiple magmatic and hydrothermal activities. We propose that gold in the arsenian pyrite from the ZZGD was scavenged in ore-forming fluids by chemical adsorption onto the As-rich, Fe-deficient, and actively growing surfaces of pyrite. Our results indicate that the primary source of the sulfur, gold, and mineralizing fluids was likely fluids from magmatic hydrothermal systems in the West Qinling orogen.

Trace element and fluid inclusion geochemistry constraint for genesis of gold-polymetallic mineralization in the Songhung deposit, DPR Korea

The Songhung deposit is located in the southwestern part of the Yangdok metamorphic core complex (YMCC) in the northern portion of the Pyongnam Basin, the eastern part of the Sino-Korean Craton. In this paper, we present a detailed study on the magma sources of the granitoids (Yangdok and Hoechang graintic intrusions), genesis of pyrite and fluid inclusion characteristics for sufficient and additional understanding of tectonic events, petrogenesis of the granitoids and mineralization in the study deposit. The Yangdok granite has lower Al2O3/TiO2 ratios (mean value of 60.58) than the Hoechang granite (mean value of 994.46), indicating the higher temperature magma source of the former. On the Rb/Ba vs. Rb/Sr and CaO/(TFeO + MgO + TiO2) vs. (CaO + TFeO + MgO + TiO2) discriminant diagrams, the magma source of the Yangdok granite belongs in the plagioclase-rich and clay-poor source rocks, while those of the Hoechang granite plots either in the plagioclase-rich and clay-poor source rocks (for granite and fine-grained granite) or in the plagioclase-poor and clay-rich source rocks (for granite porphyry and felsite). On the Nb vs. Y, Ta vs. Yb, Rb vs. Y + Nb and Rb vs. Yb + Ta tectonomagmatic discrimination diagrams, these two granites are connected with the volcanic arc-related setting and plot in post-collision setting. Moreover, some data of the Hoechang granite fall in WPG field, suggesting that the volcanic arc setting may be changed to an intraplate setting from Middle Cretaceous.The pyrite trace element geochemistry, showing the high Co/Ni ratio than one with an average of 8.2 and high Co content and low Ni content, suggests that its formation was closely linked with I-type granitic magma-derived hydrothermal fluid mixed with meteoric water. It could also be assumed by the Co and As contents in pyrite, indicating a certain degree of meteoric water in the ore forming fluid. It is consonant to the Pb, S, C and O isotope geochemistry in the previous study, suggesting that ore-forming fluids and metals could be derived from both the Yangdok granite and the Proterozoic and Paleozoic meta-sedimentary rocks exposed in the study area. All of the pyrite grains have not compositional zoning and the similar distribution patterns of Co and Ni are appeared in single pyrite grain (from core to rim), suggesting the stable crystallization environment of pyrites and same ore forming fluid source. In pyrite grains, the positive correlation between gold and arsenic is appeared. The Au exists either as a micro- and nano-size inclusion in pyrite and other minerals or as a solid solution in pyrite lattice. Based on the petrological and microthermometric characteristics of the fluid inclusions in ore-bearing quartz, we suggest that the ore-forming fluid is represented as NaCl + H2O or NaCl + KCl + H2O systems with low salinity. The absence of CO2-enriched phase and vapor-only or liquid-only primary inclusions in quartz indicates the homogenous magma-derived ore forming fluids and a lack of boiling during ore-forming process. The formation temperature and pressure of this deposit approximately vary from 317 to 326 °C and from 105.46 to 111.69 × 105 Pa, respectively, exhibiting the hydrothermal deposit origin. In conclusion, the Songhung deposit is originated from I-type granitic magma source-derived hydrothermal fluid which was mixed with meteoric water.

Structural-Morphological Types and Localization Conditions of the Apocarbonate Talc Mineralization in the Beloretsk District of the Western Urals Province

The structural–morphological types and localization conditions of talc occurrences in the Beloretsk district of the Western Urals talc province are discussed. The talc mineralization is represented by low-iron talcites and talc stones in the Riphean clastic–carbonate complexes of the Bashkirian Meganticlinorium. Prospective talc objects in the Beloretsk district are classified as apocarbonate, to be distinguished from the apoultramafic deposits, which are predominant in the Urals. The hydrothermal–metasomatic genesis of the talc ores, their association with the metamorphosed dolomite-bearing members of the Lower and Middle Riphean Kyzyltash and Avzyan formations, the cooccurrence with magnesite deposits, and the absence of relationship with granitoid magmatism are established. The inner resources of the Riphean sedimentary basins, activated by metamorphic processes, are viewed as the sources of ore-forming fluids. The flanks of magnesite bodies in dolomite sequences near contacts with silicate interbeds are considered as the lithological settings favorable for talcite formation. The presence of the stacks of interbedded magnesian–carbonate and aluminosilicate rocks in the Riphean sequences facilitates the silica–magnesium bimetasomatism but leads to the formation of predominantly lean talc–chlorite stone varieties. The morphological types of mineralization are represented by the stratiform bed-like talcite and talc stone bodies; the saddle-like and ribbon-like talcite bodies confined to monoclines and fold hinges and limbs; and the fault controlled steeply dipping linear bodies of rich talc ores.

Elemental and multiple isotopic evidences of enriched lithospheric mantle origin of the Xiadian gold deposit in the Jiaodong Peninsula, East China

The Jiaodong Peninsula is the largest gold concentration district in China and the third largest one in the world. It covers no >0.2% of China's total landmass yet accounts for 30% of the total national gold reserves with total proved resources near 5000 t Au. One wonders where all this gold comes from. Here we present detailed whole-rock element and Sr-Nd-Pb isotope, quartz H-O isotope and pyrite He-Ar isotope geochemical data for the Xiadian gold deposit, a large Jiaojia-type gold deposit in the Jiaodong district, which furnishes new constrains on the sources of ore-forming fluids and metals. The results indicate that the ore and alterated rock have much higher HREE (e.g. Yb and Y), HFSE (e.g. Nb, Ta, Zr and Hf) and transition elements (e.g. Sc, Ti, V, Cr, Co and Ni) than the host granites but similar to the lithospheric mantle-derived lamprophyres, suggesting an enriched lithospheric mantle origin. The H-O isotopes (δDV-SMOW = −93.9‰ to −102.3‰, δ18OH2O = −0.2‰ to 1.6‰) of fluid inclusions in quartzs collected from auriferous pyrite–sericite–quartz altered rocks are distinctly different from either primary magmatic water and metamorphic water or meteoric water in the Jiaodong district but similar to the local enriched mantle-derived fluids. The He-Ar isotopes [3He/4/He = 0.58 × 10−6 to 1.90 × 10−6 (0.42–1.36 Ra), 40Ar/36Ar = 725–1358] of fluid inclusions in pyrites collected from auriferous pyrite–sericite–quartz altered rocks are also similar to the local enriched mantle-derived fluids. The ore and alterated rock have distinct Nd-Pb isotopic compositions either from the host Linglong granites or from the asthenosphere-derived mafic dikes but similar to the lithospheric mantle-derived mafic dikes. Their Sr isotopic compositions show a mix trend between the lithospheric mantle-derived mafic dikes and Neoarchaean basement. All the elemental and multiple isotopic features support a metallogenic model that the ore-forming fluids and metals were derived from the local previously enriched lithospheric mantle, and such deeply sourced fluids may have interacted with Neoarchaean basement along their flow path and mixed with a little meteoric water when they arrived high levels in the crust.

Trace elements of pyrite and S, H, O isotopes from the Laowan gold deposit in Tongbai, Henan Province, China: implications for ore genesis

The Laowan deposit is a large gold deposit in the Qinling-Dabie orogenic belt where pyrite is the main Au-bearing mineral phase. We present results from the occurrences of gold, trace elements and sulfur isotopes of pyrite, and hydrogen and oxygen isotopes of quartz and calcite to elucidate the sources of ore-forming fluid; the genesis of pyrite and the ore-forming process. From field observations, five generations of pyrite are identified; one formed in a metamorphic-diagenetic epoch (PyI), and the others during four mineralization stages: 1) the coarse-grained pyrite-quartz stage (PyII), 2) the quartz and medium- to fine-grained pyrite stage (PyIII), 3) the polymetallic sulfide stage (PyIV), and 4) the carbonate-quartz stage (PyV). Gold mainly occurs in PyIII and PyIV. We find that Au, Ag, Pb, and Cu are incorporated into pyrite as micro-/nano-inclusions and that Co, Ni, As, and Se enter the pyrite lattice via isomorphous replacement. The Co/Ni values and Se concentrations indicate that PyI formed from metamorphic hydrothermal fluids and that pyrites (PyII, PyIII, and PyIV) from the ore-forming stages typically reflect a hydrothermal genesis involving magmatic fluid. The δ34S values of PyI (1.45 ‰–2.09‰) are similar to that of plagioclase amphibole schist, indicating that S was primarily derived from wall rock, while those of PyII, PyIII, and PyIV (3.10‰–5.55‰) suggest that S was derived from the Guishanyan Formation and the Laowan granite. The four mineralization stages show a systematic decrease in δD (from −77.1‰ to −82.8‰, −84.7‰, and −102.7‰), while the $${{\rm{\delta }}^{18}}{{\rm{O}}_{{{\rm{H}}_2}{\rm{O}}}}$$ values showed a gradual decrease from 5.7 to 2.7‰, 1.0‰, and −1.3‰. These data show that the ore-forming fluid was similar to a mixture of magmatic and meteoric waters. Thus, we conclude that the Laowan gold deposit is related to magmatic-hydrothermal fluid.

Ore-forming fluid source of the orogenic gold deposit: Implications from a combined pyrite texture and geochemistry study

Interpretation of bulk sulfur isotope data of the orogenic gold deposit is frequently hampered by complex zoning in pyrite, which calls for in-situ determination of sulfur isotope composition of sulfide minerals. The Qiuling gold deposit, located in Qinling orogen, is representative of orogenic type and selected here to further constrain the source of sulfur (and Au) and test the current popular ore genesis models for deposits of this type. Detailed backscattered electron imaging (BSE) study is applied to characterize intragrain texture, and subsequently in-situ sulfur isotope and trace element determination using secondary ion mass spectrometry (SIMS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) are used to reveal sulfur and metal source and evolution of the ore-forming fluid.Two generations of pyrite, i.e., pre-ore stage (Py1) and ore stage pyrite (Py2), were investigated in this study. In most cases, Py1 occurs as pyrite framboids, while Py2 as euhedral grains, in which Py2a as anhedral core, Py2b and Py2c as euhedral inner and outer rim, respectively. The δ34S values of both Py1 and Py2 have unusual wide ranges, i.e., a δ34S variation from −31.1 to +106.7‰ for Py1 (average +0.8‰) and from −2.7 to +24.1‰ for Py2 (average +13.2). The distribution pattern of δ34S values in Py1 is accommodated with Rayleigh fractionation in sulfate-restricted pore water. Modeling results show that neither temperature nor oxygen fugacity change could result the variations in δ34S values of Py2, and contribution of both preexisting pyrite and a pulse of ore-forming fluid with δ34S about +14.2‰ may be responsible for the observed variation in Py2. Such fluid may have been sourced from metamorphism of old strata such as the Neoproterozoic basement. Furthermore, Py2a shows an intimate relationship with Py1 in its δ34S values, indicating Py1 may have acted as part of sulfur source in the formation of Py2a.Py1 is rich in a suit of element such as Bi, Co, Mn, Ni, Tl and has the lowest As and Au. Py2a is similar with Py1 but with elevated As and Au. Py2b contains more abundant As and Au compared to Py2a. Py2c is rich in As and especially Au, but depleted in other elements compared to Py2a. The distribution pattern, coupled with sulfur isotope composition, indicates that Py2a was likely formed with a contribution of trace elements and sulfur from Py1 at the start of hydrothermal process. Py2b was formed with elevated proportion of contribution from the ore-forming hydrothermal fluid, while Py2c was formed solely by the ore-forming fluid without a contribution from previous pyrite. Consequently, the ore-forming fluid in the Qiuling gold deposit was rich in As, Au, Cu and Sb while depleted in other metals such as Bi, Co, Mn, Ni and Tl, indicating that the pre-ore framboid pyrite may have not contributed any Au and As during mineralization.This study highlights the importance of detailed texture characterization coupled with relatively large data set of in-situ sulfur isotope and trace elements for orogenic gold deposit research, and further proves that metamorphic fluids may have significant contribution for Au mineralization in orogenic gold deposits.

Formation conditions, composition and ore-forming sources of the Bolshoy Karan gold-porphyry deposit (the Southern Urals)

Research subject. We studied PT conditions, composition and sources of ore-forming fluids of the Bolshoy Karan goldporphyry deposit (South Urals) confined to the Main Urals Fault zone at Southern Urals. Methods. Temperatures of ore mineral formation, salt composition and fluid salinity were estimated using a Linkam TMS-600 cryostage equipped with an Olympus BX 51 optical microscope. The gas composition of fluid inclusions was determined using a Horiba LabRam HR800 Evolution Raman spectrometer and an Olympus BX-FM optical microscope. Trace elements were detected by means of LA-ICP-MS analysis. С and О isotopic composition was identified using a MAT 253 (Thermo Fisher Scientific) mass-spectrometer. S in the minerals of sulphide-carbonate-quartz ores was identified using a Delta PLUS Advantage mass-spectrometer. Results. It is shown that the fluid inclusions in quartz are homogenized at 370–310oC, while those of the latest calcite – at 234–200oС. The fluids contain Mg-Na chloride solutions with a salinity of 3.0–11.9 wt % NaClэкв. According to LA-ICP-MS data, quartz contains high Al contents (916–1556 ppm) confirming its formation from a high aluminous acid fluid. The REE distribution spectra in calcite are characterized by the accumulation of light lanthanides (La N /Yb N = 3.4–9.11) pointing to the acid fluid composition, as well as by negative Ce (0.58–0.88) and positive Eu (1.51–3.61) anomalies. The negative Ce anomaly may have been caused by interactions between the fluid and host limestones. The positive Eu anomaly reflects the existence of a middle-temperature environment (>250oC) prior to calcite crystallization. Y/Ho values in calcite (29.3–35.6) suggest the presence of magmatic components and those extracted from limestones. The values of δ 18 О in calcite vary from 14.7 to 19.8‰, while those of δ 13 С – from –4.1 to 0.7‰. The values of δ 18 О H 2 O for the ore-forming fluid, which were calculated based on average homogenization temperatures of fluid inclusions in calcite (230oС), vary from 6.5 to 11.5‰, while δ 13 С СO 2 – from –3.21 to 1.6‰. δ 34 S values in pyrite ranged from –0.60 to – 1.50‰. Conclusions. Our data confirm the formation of the gold-porphyry mineralization of the Bolshoy Karan deposit under mesothermal conditions. Magmatic fluids played the key ore-formation role. The geochemical peculiarities of interactions between the fluid and host rocks were revealed.

Ore-Forming Fluids of the Aleksandrovskoe and Davenda Deposits (Eastern Transbaikalia)

A study of the composition of fluid inclusions in ore minerals of the Davenda Mo–porphyry deposit and the Aleksandrovskoe sulfide–quartz–gold ore deposit, as well as of fluid inclusions in minerals of igneous rocks, showed that ore-forming fluids inherit the salt and gas composition of magmatic fluids generated during crystallization of ore-bearing rocks of the Amudzhikan–Sretensky Igneous Complex, which formed simultaneously with the Au and Mo mineralization. The gold-bearing sulfide–quartz veins of the Aleksandrovskoe deposit formed with the participation of two types of hydrothermal fluids, differing in the composition of salts and the gas phase: homogeneous Ca–Na chloride fluids with CO2 and heterophasic Na–K–Fe-chloride fluids, which indicates two sources of ore-forming fluids during the formation of Au-mineralization. Na–K–Fe-chloride fluids in terms of salt and gas composition were similar to the ore-forming fluids of the Mo-mineralization of the Davenda deposit. Ore-forming Ca–Na-chloride with CO2 The fluids of the Aleksandrovskoe field are comparable in salt and gas composition with the magmatogenic fluids of quartz diorite porphyries and diorite porphyrites. Ore forming Na–K–Fe carbonate-chloride fluids of the Davenda and Aleksandrovskoe deposits show great similarity in composition to magmatic fluids of granite porphyry and emphasize the genetic identity of Mo mineralization in both deposits. The data obtained confirm the widespread opinion that a genetic relationship exists between gold mineralization and dikes of intermediate and mafic composition, and molybdenum–porphyry mineralization with granite–porphyry of the Amudzhikan–Sretensky Igneous Complex. The real agents of this genetic link are metalliferous magmatogenic fluids, the salt and gas composition of which inherit ore-forming fluids. The formation depth of productive ore mineral assemblages in veins of the Aleksandrovskoe and Davenda deposits is estimated at 7.9–7 and 8–6.3 km, respectively, which is not typical of porphyry deposits, the formation of which is characterized by shallower depths.

The Middle Permian Hongshanliang Manto-type copper deposit in the East Tianshan: Constraints from geology, geochronology, fluid inclusions and H–O–S isotopes

The Hongshanliang copper deposit, hosted in the tuff of the Lower Carboniferous Yamansu Formation, is a typical copper deposit in the Aqishan–Yamansu belt, East Tianshan. Based on crosscutting relationships of veins, textural relationships and mineral assemblages, five alteration/mineralization stages at Hongshanliang have been established: chlorite–sulfide stage (Stage I), quartz–pyrite stage (Stage II), quartz–polymetallic sulfide stage (Stage III), late veins (Stage IV) and supergene process (Stage V).Stage I has mineral assemblage of chlorite–pyrite ± chalcopyrite ± quartz ± sericite, and is commonly characterized by euhedral pyrite with silicates (e.g., chlorite, quartz and sericite) and/or chalcopyrite as its pressure shadow, indicating an early mineralization event with apparent deformation. Stage II is characterized by quartz–pyrite ± chalcopyrite or locally quartz ± gypsum ± anhydrite ± pyrite veins cutting Stage I chlorite–pyrite. The main mineralization stage (Stage III) at Hongshanliang has typical mineral assemblages of quartz–chalcopyrite ± chlorite ± calcite ± sericite, quartz–chalcopyrite–sphalerite–galena ± pyrite and quartz–sphalerite–galena ± chlorite, with veins, veinlets, disseminations and local massive ore types, similar to Manto-type copper deposits regarding mineralization and ore structures. Detailed fluid inclusion study shows temperature of fluids decreased from Stage II (307–484 °C) through Stage III (peak at 160–180 °C, consistent with quartz–chlorite oxygen isotope geothermometer of 190 °C) to Stage IV (129–169 °C), with corresponding salinities of 2.7–26.2 wt% NaCl equiv. (peak at 8 wt%), 2.1–12.3 wt% NaCl equiv. (peak at 8 wt%) and 0.5–7.7 wt% NaCl equiv. (peaks at 4–6 wt%), respectively, indicating an evolved hydrothermal ore-forming system. Such fluid evolution can also be supported by H–O isotopes during water–rock reaction from Stage II (δ18Ofluid = 6.3–8.3‰ and δDfluid = −77‰ to −64‰) through Stage III (δ18Ofluid = − 1.7‰ to 7.0‰ and δDfluid = − 82‰ to − 58‰) to Stage IV (δ18Ofluid = − 2.5‰ to − 2.1‰ and δDfluid = − 77‰ to − 73‰) with a magmatic–hydrothermal origin. Furthermore, sulfur isotopes suggest that fluids of the two mineralization stages (Stage I and III) are predominantly magmatic–hydrothermal, with other influx contribution into the ore-forming system, i.e., minor Early Carboniferous seawater in Stage I (δ34Sfluid varying from − 3.5‰ to 6.1‰, with peak at 0‰) and minor organic materials in Stage III (δ34Sfluid varying from − 6.5‰ to 4.1‰, with peak at 0–1‰, and detection of CH4 and C2H6 from fluid inclusions).In combination of alteration, paragenesis, nature and source of ore-forming fluids and comparison with other typical deposits, we proposed that the Hongshanliang copper deposit underwent two mineralization events with the main mineralization similar to Manto-type copper deposits. 40Ar/39Ar dating of sericite from a massive chalcopyrite ore indicates the Hongshanliang main mineralization formed at 269.0 ± 0.4 Ma, generally coeval with regional K-feldspar granite emplacement (ca. 272 Ma). Integrating the regional tectonic setting, magmatism and metallogenesis of the Aqishan–Yamansu belt and the East Tianshan, we suggest that the Aqishan–Yamansu belt has potential of mineral prospecting for the Middle Permian Manto-type copper deposits.

Sources of Ore-Forming Fluids and Materials of Gold and Antimony Deposits in Southwestern Guizhou

Sources of Ore-Forming Fluids and Materials of Gold and Antimony Deposits in Southwestern Guizhou