Gold Orebodies Research Articles

The relationship between Carlin-type Au mineralization and magmatism in the Youjiang Basin-a case study from the Mingshan gold deposit in northwest Guangxi, China

The Youjiang Basin in Southwest (SW) China is the second-largest Carlin-type goldfield in the world after Nevada, USA; however, the spatial, temporal, and genetic links between Carlin-type Au mineralization and magmatism in SW China remain controversial compared with those in Nevada. The Mingshan gold deposit is one of the few Carlin-type gold deposits that exhibits a close spatial relationship between gold orebodies and magmatic rocks in the Youjiang Basin. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) uranium-lead (U-Pb) dating of magmatic zircons from quartz porphyry dikes and hydrothermal apatite associated with gold yields the intrusive and gold mineralization ages of 96.34 ± 0.89 and 139.9 ± 4.8 Ma, respectively, indicating that the magmatism was much younger than the gold mineralization at Mingshan. Petrography and microthermometry of the fluid inclusions from ore-stage quartz and calcite suggest a low to moderate temperature (140–240 °C), low salinity (3–8 wt% NaCleqv), and moderate to low density fluid. The hydrogen and oxygen isotope compositions of the ore-stage quartz indicate a metamorphic fluid source of the ore fluid. Thus, we propose that the close spatial contact between the gold orebodies and igneous dikes could have resulted from the same NWW-trending fault space during the Early Cretaceous precipitation of ore fluid and the Late Cretaceous intrusion of the quartz porphyry dikes. However, the genetic link between the quartz porphyry and Carlin-type Au mineralization was not observed at Mingshan. The primary metamorphic fluid associated with Early Cretaceous gold mineralization in the Youjiang Basin was derived from syn-orogenic shortening deformation and metamorphism in the compressional tectonic setting caused by the subduction of the Paleo-Pacific Plate. Subsequent post-orogenic extension during the rollback of the subducted Pacific slab led to significant extensional faults and intrusions of Early Cretaceous concealed granites, which may have provided heat, materials, and energy for the transport of ore fluid. The ore fluid was transported through permeable extensional structures from the deep crust and reacted with the carbonaceous and Fe-rich host rocks in the shallow crust, resulting in the Early Cretaceous gold mineralization event in the Youjiang Basin.

Role of metasomatized mantle lithosphere in the formation of giant lode gold deposits: Insights from sulfur isotope and geochemistry of sulfides

The Wulong deposit is one of the largest quartz vein-type gold deposits with at least 80 tons of identified gold reserves in the eastern part of the Liaodong Peninsula. Gold orebodies are mainly hosted in the Late Jurassic gneissic two-mica granite and Early Cretaceous diorite dykes, and are structurally controlled by the NNE- and NW-trending faults. Gold mineralization mainly occurs as veins with lenticular shapes and is closely associated with sulfides and Bi minerals. Previous studies on the deposit mainly focused on its geological characteristics, fluid inclusions and the timing of gold mineralization. However, the extreme enrichment mechanism of gold, the geodynamic setting and ore source of the gold deposit remain equivocal. Here we present results from geochemical studies of pyrite and pyrrhotite at Wulong to address these issues. Pyrrhotite can be grouped into euhedral (Po1) and anhedral (Po2) varieties based on the textures. Four generations of pyrite were identified based on petrographic studies: Py1 is coarse-grained subhedral to euhedral crystal coexisting with milky quartz, and Au-depleted in composition; Py2 is represented by medium-grained, subhedral to anhedral pyrite coexisting with euhedral Po1, smoky quartz and minor chalcopyrite; Py3 occurs as fined-grained anhedral grains in the quartz-polymetallic sulfide veins; Py4 occurs as veinlets or aggregates in the quartz-calcite veins and contains the lowest Au concentrations. The time-resolved LA-ICP-MS ablation depth profiles of sulfides combined with detailed petrological observations indicate that gold mainly occurs either as invisible solid solution within the crystal lattice of sulfides, to some extent, or as small blebs of native gold and electrum. The close temporal and spatial relationships among native bismuth, native gold and Bi-Te-S minerals suggest that Bi-rich melts may have significantly sequestered gold from the hydrothermal fluids in the Wulong gold deposit. Sulfides from auriferous quartz veins have a restricted Δ33S range (−0.2‰ to +0.2‰) and a mean δ34S value of +1.25‰ with a feature of the mass-dependent fractionation (MDF) of sulfur isotopes, implying that the ore-forming materials were potentially derived from the mantle lithosphere that was metasomatized and fertilized by subduction-related fluids released from slab during the Early Cretaceous. This study demonstrates the Bi-rich melts as significant gold scavengers in As-deficient ore-forming fluid, and highlights the fundamental role of the metasomatized and fertilized mantle lithosphere in the formation of giant lode gold deposits in the eastern North China Craton at ca. 120 Ma.

The Improvement and Application of the Electrogeochemical Exploration Method

The anionic and cationic species of elements from deeply buried deposits migrate to the near surface driven by various geological forces. The applied electric field is used to collect these active ions to the designed electrode, and ions with a negative charge go to the anode and positive to the cathode, which is called electrogeochemical exploration method, also called CHIM. Prospecting effect has been investigated by researchers since the coming up of CHIM. However, the cumbersome technical equipment, complex techniques and low production efficiency have restricted its potential application in field geological survey. This paper presents the newly developed CHIM alternatives that are electrified by a low voltage dipole. The improved technique allows both anionic and cationic species to be extracted simultaneously in an anode and in a cathode. Compared with the conventional CHIM method, the innovative techniques called dipole electrogeochemical method are characterized by simple instrumentation, low cost and easy operation in field, and in particular enables simultaneous extraction of anionic and cationic species of elements, from which more information can be derived with higher extraction efficiency. The “dipole” electrogeochemical extraction method was proposed and applied in the experiments of the Yingezhuang gold ore in Zhaoyuan, Shandong Province, the 210 gold ore in Jinwozi, Xinjiang Province, and the Daiyinzhang gold polymetallic deposit in Wutaishan, Shanxi Province. There are clearly anomalies above the gold ore body, indicating the effectiveness and feasibility of the improved dipole electrogeochemical method in both scientific research and mineral exploration. The results of anode extraction in several mining areas have shown good results, indicating that gold may be mainly negatively charged. In fact, many metal nanoparticles, clay minerals, or complexes of metal ions are negatively charged, so they migrate to the anode electrode and enrich.

Ore-forming materials and fluids and ore-controlling factors of the Liaoshang gold deposit in Jiaodong Peninsula, NE China

The Jiaodong Peninsula is the most important gold province in China, and the Liaoshang gold deposit represents a major recent prospecting breakthrough in Jiaodong.Based on detailed metallographic and microstructural observations, and He-Ar-Pb isotope compositions of fluid inclusions from main-ore-stage pyrite were presented, as well as the CO isotope compositions of main-ore-stage dolomite. Fluid inclusions from the pyrite have 3He = 1.18 – 8.69 × 10-14 cm3STP/g, 4He = 1.21 – 3.24 × 10-7 cm3STP/g, and 3He/4He = 0.12 – 0.81 Ra, and the ore-forming fluid was mainly crustal-sourced with mantle fluid input. The fluid inclusions have 40Ar = 5.42 – 1.87 × 10-7 cm3STP/g, 40Ar/36Ar = 328.5 – 511.3, close to saturated meteoric water 40Ar/36Ar value. It is speculated that the crustal-sourced ore fluid may have had meteoric water input in the mineralization. The main-ore-stage dolomite contains δ13C = -2.9 to −4.4 ‰ and δ18OV-SMOW = 10.5 to 11.3 ‰. It is speculated that the carbon was mainly deep magmatic fluid- or magma-sourced. The pyrite has 206Pb/204Pb = 17.244 – 17.416, 207Pb/204Pb = 15.448 – 15.462, 208Pb/204Pb = 37.824 – 37.950, and 206Pb/207Pb = 1.116 – 1.125, indicating that the ore-forming materials were derived from a crust-mantle-mixed source, which we considered to be the Linglong granite and the Jiaodong (or Jingshan) Group wallrocks. We conclude that the ore-forming fluids and materials at Liaoshang have multiple and complex sources, and that the Mesozoic tectono-magmatic activities have a clear control on the formation and distribution of the Liaoshang gold orebodies..

New insights into the genesis of the Sipingshan gold deposit in eastern Heilongjiang, north-eastern China: Evidence from geology, U-Pb and Rb-Sr geochronology, geochemistry, and H[sbnd]O[sbnd]S-Pb isotopes

The Sipingshan gold deposit is intermediately sized and located in the eastern Wandashan Terrane. It has attracted much attention for its uncommon genetic type of hot spring. Gold orebodies mainly occur in the upper and lower siliceous rocks, siliceous cemented breccia is found between the upper and lower siliceous rocks, and silicified rhyolite porphyry is observed below the lower siliceous rocks. Two main mineralisation periods (i.e. exhalative sedimentation and hydrothermal superimposition) have been identified at Sipingshan based on mineral paragenesis and crosscutting vein relationships. In this study, analyses of whole-rock geochemical compositions, pyrite Rb–Sr age, zircon U–Pb–Hf contents, and S–PbOH isotopes were conducted to determine the Au mineralisation time and ore genesis of this deposit. The ore-bearing siliceous rock revealed weighted mean 206Pb/238U ages of 121.8 ± 1.1 Ma and 117.6 ± 1.0 Ma, representing the mineralisation age of the exhalative sedimentation period. The Rb–Sr isochron age of pyrites (106 ± 3 Ma) was consistent with the Au–Cu mineralisation age in the Wandashan area and represented magmatic–hydrothermal mineralisation. The siliceous rocks were characterised by high SiO2 (97.92–99.18 wt%), low TiO2 (0.01–0.03 wt%), low Al2O3 (0.22–0.55 wt%), negative δCe (0.78–1.00), positive δEu (1.12–4.04), and low Sb, As, Cs, Cd and Li contents, indicating the genesis of hydrothermal sediments. The OH isotope results suggested that the ore-forming fluids were mainly derived from magmatic water and mixed with meteoric water in the later stage. The δ34S values of pyrites from the siliceous rocks (–25.8 to –8‰) indicated a biogenic sulfur-dominated source, corresponding to the exhalative sedimentation period. The δ34S values of pyrites (9.8 to 29.7 ‰ and –1.9 to –4.7 ‰) formed in the magmatic–hydrothermal period indicated that sulfur was most likely derived from sedimentary rock and magmatic sulfur sources. The Pb isotope data also implied a mixture of upper crust and mantle sources. Therefore, we propose that the Sipingshan gold deposit is a continental exhalative sedimentation-type gold deposit superimposed by later magmatic–hydrothermal fluids, and formed during the subduction of the Paleo-Pacific Plate during the Early Cretaceous.

Genesis of the Yangjiakuang gold deposit, Jiaodong peninsula, China: Constraints from S-He-Ar-Pb isotopes, and Sm-Nd and U-Pb geochronology

Located in the Penglai-Qixia-Fushan Gold Belt, the Yangjiakuang gold deposit formed in the marble of the Paleoproterozoic Fenzishan Group is different from the previous altered rock-type gold deposits whose host gold-bearing rocks are Archean gneiss and Mesozoic granite. Two gold orebodies have been explored within the Yangjiakuang gold deposit, and both of them were controlled by the Yangjiakuang syncline. Three ore-forming stages have been recognized, including the pyrite-sericite stage (I), the gold, polymetallic sulfide, and quartz stage (II), and quartz-calcite stage (III). The calcites, which represent the main metallogenic stage (II) at Yangjiakuang gold deposit, yielded a Sm-Nd isochron age of 123.5 ± 8.1 Ma (MSWD = 0.042). Subsequent geologic events were recorded by quartz diorite porphyrite dyke which are dated at 122.75 ± 0.66 Ma (MSWD = 1.5) by zircon LA-ICP-MS U-Pb dating. It is suggested that the gold mineralization took place in the early period of Early Cretaceous. The in situ δ34S values of pyrites from two stages have a narrow range from + 5.65 to + 9.63‰ with an average value of 8.14‰, which indicate that the source of δ34S is related to the Guojialing granite and the Fenzishan Group. The lead isotopic compositions of pyrites (206Pb/204Pb = 16.615 to 16.832; 207Pb/204Pb = 15.275 to 15.403; 208Pb/204Pb = 36.829–37.470) show a consistent origin of the lower crust. The measured 3He/4He (40Ar/36Ar) of hydrothermal fluids in pyrites are 0.641–1.132 Ra (637.5–1162.7), indicating that the ore-forming fluid originating from a mixing of crustal and mantle components. It is suggested that the gold mineralization is associated with extensional tectonic inversion caused by the rollback of the subducting Izanagi Plate during the early Cretaceous, which triggered partial melting of mantle and lower crust, and subsequent magma mixing and exsolution of ore-bearing fluids. These fluids extracted ore-forming materials from the enclosing rocks of the Jiaodong Group, the Fenzishan Group, and the Guojialing granite to form the ore-forming fluids.

Conditions of formation and stages of mineralization of the Pyazbashi gold-sulfide-quartz deposits (Leser Caucasus, Azerbaijan)


 
 
 We analyzed the conditions of the formation and stages of mineralization of the Pyazbashi gold-sulfide-quartz deposits. The deposits were determined to contain three structural-morphologic types of ore bodies: gold-quartz-sulfide – veinular, gold-bearing veins and the strip of gold-bearing metasomatites. We determined that in the deposits, quartz-pytire, quartz-carbonate and carbonate veins with gold and polymetal mineralization are confined to the volcanic-tectonic structures. Those volcanic-tectonic structures have various fracture systems, are complicated and have been inherited by later changes that occurred after the formation of the Lower and Middle Eocene volcanogenic complexes, and some of them have been embedded again. We de- termined that gold ore mineralization in the deposits is related to various hydrothermal-metasomatic formations and has developed in complex multy-stage process. Interaction of various veins and minerals that comprise them allow us to assume the following pattern in the sequence of the mineralization stages (from early stage to later stages): 1-quartz-sericite; 2-quartz-pyrite-molybdenum; 3-quartz- pyrite-gold ore; 4-quartz-polymetal; 5-carbonate. Gold-ore bodies are mainly complicated by aggregates of quartz-pyrite-gold ore stage of mineralization, which is the productive stage. We present the results of chemical analysis of native pyrite and chalcopyrite. We determined that native gold occurs as small, regular-shaped bodies in pyrite grains. In the veinlets of chalcopyrite, it is usually confined to marginal parts.
 
 

Age, geochemistry, mineralization, and tectonic significance of felsic‐intermediate dikes in Shuangqishan Au deposit, Cathaysia block, South China

AbstractThe Shuangqishan Au deposit (>15 t) is located in the Dehua‐Youxi‐Yongtai goldfield of the southeastern Cathaysia Block, South China. There are three stages of granites in the Shuangqishan Au deposit, the pre‐mineralization granite porphyry formed in the Middle Jurassic (~166.0 ± 0.8 Ma), the metallogenic granite porphyry and monzonite porphyry formed in the late stage of the Late Jurassic (153–151 Ma), the post‐mineralization granites (granite porphyry, the masanophyre, the dioritic porphyrite) formed in the Early Cretaceous (129.0–120.0 Ma). All rocks are characterized by high‐K calc‐alkaline and shoshonities series, the per‐mineralization granites are enriched in Rb, Th, K, Zr, and Hf, depleted in Ba, P, and Ti, significant negative Eu anomaly and distinctly tetrad effect with highly fractionated I‐type granitoids characteristics. The metallogenic granites and the post‐mineralization granite porphyry are enriched in K, Rb, Th, Ce, Zr, Hf, and Y, enriched in LREE, strongly depleted in Sr, Ba Ta, P, Ti, have moderate negative Eu anomalies with I‐type granites characteristics. However, the post‐mineralization dioritic porphyrite displays strong depletions Sr, Ta, P, and Ti whereas Rb, Th, Ce, and Sm are enriched, enriched in LREE with weakly negative Eu anomalies. The metallogenic granite porphyry is significantly enriched in Au, As, Sb, W, Mo, and Bi, especially enriched in Au. The Lu‐Hf isotopic data indicate that the magma source comes from the partial melting of the Paleoproterozoic crust, the minor part from the mantle in the Early Cretaceous. Therefore, we propose that the granitoids formed in the subducted plate environment from the Middle Jurassic to the Early Cretaceous, the Late Jurassic I‐type granites (~153–146 Ma), The Shuangqishan Au deposit was formed in the stage from compression to extension, the Early Cretaceous granites (~129–114 Ma) mainly formed in the extensional environment and destroyed gold ore bodies.

Spatial coupling relationship between faults and gold deposits in the Jiaodong ore concentration area and the effect of thermal doming-extension on mineralisation

As the third largest gold ore-forming province in the world, the deep metallogenic potential of and exploration strategies for Jiaodong gold deposits have attracted substantial attention. By applying three-dimensional (3D) geological modelling to these super-giant and giant gold deposits, this study reveals the 3D morphological characteristics of the ore-bearing faults and the ore-related granites, analyses the relationships between ore body locations and slope dip angle changes in the faults, and discusses the coupling relationships among gold mineralisation, ore-controlling faults, and magmatic activities. In the 3D model, the dip angles of ore-controlling faults gradually decrease downwards and alternate between steep and gentle along the fault dip direction. The ore bodies mainly occur in areas with relatively high fault-dip-angle change rates. Hence, positions with fault dip angles of 20°–50° and change rates of ≥0.91 should be considered as target areas for prospecting deep gold ore bodies. In-depth analysis suggests that the ore-hosting faults, granites, and gold mineralisation resulted from regional thermal doming and extensional movements. Gold ore bodies in the Jiaodong Peninsula occur inside or on the periphery of Mesozoic granite. Strong magmatic activities during the transition from enriched to depleted mantle provided the necessary metallogenic and thermal dynamic environment for gold mineralisation. In particular, the magmatic evolution provided abundant ore-forming materials. The detachment faults with varied dip angles provided favourable space for gold mineralisation, as the fluctuations of ore-forming fluid pressure caused by sudden changes in these dip angles served as the primary mechanism underlying the step-like gold mineralisation pattern.

Fluid inclusion and stable isotope (H–O–S–Pb) constraints on the genesis of the Haxi gold deposit, west Junggar, China

The Haxi gold deposit located in the Hatu–Saertuohai metallogenic belt of the west Junggar region, China, is a newly discovered gold deposit with proven reserves of ∼10 tons of gold and an average grade of 6.70 g/t. Primarily, the deposit is hosted in the early Carboniferous Tailegula Formation, controlled by the NEE-trending Anqi fault. The gold ore bodies contain gold-bearing quartz veins and altered basalt. The ore mineral is dominated by abundant sulfides, such as pyrite, arsenopyrite, chalcopyrite, and a little gersdorffite. To date, three types of fluid inclusion in quartz veins have been identified: liquid–gas (V-type), CO2–H2O (C-type), and liquid–rich (L-type). The ore-forming fluids exhibit medium homogenization temperatures (Th) of 226 °C–325 °C with low salinities of 2.24–9.34 wt% NaCl equivalent and low densities from 0.72 to 0.88 g/cm3. The δD values range from −115.3‰ to −100.7‰, with an average value of −109.1‰; the δ18O values range from 11.3‰ to 12.2‰, with an average value of 11.8‰; and the δ34S values in sulfide range from 0.3‰ to 1.8‰, with an average of 1.2‰. The average values of 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb in sulfide are 18.059, 15.547, and 37.996, respectively. To summarize, the metallogenic fluids were derived not from a single source but from late magmatic–hydrothermal fluid mixed with paleo-atmospheric water; furthermore, the ore-forming materials principally originated from a crust–mantle mixed source. The Pb model age calculated using Hautman’s formula is 347–365 Ma, leading to the speculation that the metallogenic period may be Devonian–Carboniferous.

Seismic imaging of the gold deposit and geological structures through reprocessing of legacy seismic profiles near Kloof–Driefontein Complex East Mine, South Africa

AbstractTwo legacy reflection seismic profiles were acquired in 1988, north of the Kloof–Driefontein Complex East Mine in the West Rand goldfield (South Africa), for the purpose of gold exploration and mine planning. These legacy 2D seismic data have been reprocessed using the latest processing tools to improve imaging. Special interest is given to the Black Reef Formation, which hosts a known gold orebody. The original legacy data are of poor quality, especially in areas that are dominated by dolomitic outcrops. To improve the quality of the data, special attention was given to the refraction static correction to enhance the continuity of the reflections below dolomitic rocks. Refraction seismic tomograms from both profiles exhibit three‐layer P‐wave velocity models: (1) topsoil (1000–2000 m/s), (2) a weathered layer ranging from ca. 100 to 300 m in thickness (2000–5000 m/s) and (3) bedrock (> 5000 m/s). Seismic profile OK‐212 shows poor imaging of the Black Reef Formation because of the scattering of seismic energy in the near‐surface due to dolomites from the Transvaal Supergroup, while seismic profile OK‐213 exhibits south‐dipping reflections that are associated with the Black Reef Formation. To improve the structural imaging resolution, we tried pre‐stack time migration, pre‐stack depth migration and post‐stack time migration using the Kirchhoff algorithm. PreSDM most improved the imaging of deeper reflections due to its ability to honour complex lateral variations in the velocity field. Both pre‐stack time migration and post‐stack time migration enhanced the continuity of the near‐surface reflections below the dolomitic rocks.

The Formation of the Jiaodong Gold Province

AbstractGold deposits in Jiaodong, termed Jiaodong‐type, are tectonically located in the southeastern margin of the North China Craton. Their major features are reviewed in this paper to highlight the differences between Jiaodong deposits and other genetic types of gold deposits. The mineralization was synchronized with asthenosphere upwelling indicated by syn‐ore OIB‐like mafic dike and large‐scale crustal thinning suggested by decrease of Sr/Y from pre‐ore to syn‐ore granites. Asthenosphere upwelling induced by the roll‐back of Paleo‐Pacific Plate drove partial melting of lithospheric mantle and devolatilization, which induced the release of the ore‐forming fluids. In concomitant with magmatic records, mineralization migrated from the western Jiaobei terrane (133–127 Ma) to the eastern Sulu orogenic belt (114–108 Ma), corresponding to the eastward roll‐back of Paleo‐Pacific Plate. Gold mineralization in Jiaodong formed in the transitions of ductile to brittle deformation, rapid to slow crustal uplift, and regional compression to extension. In the regional‐scale, the gold deposits in the Jiaobei terrane are mostly situated at intersections between NE‐trending faults and EW‐trending basement faults, and gold orebodies dominantly controlled by the lithologic contacts between Precambrian metamorphic rocks and Mesozoic granites. The mineralization was dominated by the disseminated‐veinlet ores related to quartz–sericite alteration in strong cataclasite‐breccia zone, with subsidiary thick quartz‐sulfide veins developed in secondary fault zones. The ore‐forming fluids belong to a H2O–CO2–NaCl±CH4system and show minor variations in salinity among different types of ore. Structure‐fluid feedback involving fluid‐rock reaction and hydrofracturing triggered the fluid phase separation and resultant gold deposition. The Jiaodong gold deposits are distinct from orogenic and intrusion‐related gold deposits in terms of tectonic setting, origin of ore‐forming fluids, and mechanism of gold deposition.

Textures, trace elements, sulfur, lead and He-Ar isotope analyses of pyrite: Implications for ore-forming processes and the origin of the Shenjiayao gold deposit, southern margin of the North China Craton

The Shenjiayao gold deposit (8.50 t Au, average grade of 2.21 g/t), hosted in a Precambrian metamorphic terrane, is located in the Xiaoshan region on the southern margin of the North China Craton. The gold mineralization is characterized by vein ores comprising native gold and gold-bearing pyrite. Paragenesis of the Shenjiayao deposit can be divided into four stages. Stage I is pyrite – milky quartz veins; Stage II consists of grey quartz – pyrite veins; Stage III is characterized by quartz – polymetallic sulfide veins; and Stage IV minor pyrite – carbonate – quartz veins. Native gold and electrum grains are mainly distributed in the fractures of quartz, pyrite, chalcopyrite, and other sulfides. In this study, three types of pyrite were distinguished based on textural and geochemical results. Py1 has silicate inclusions and mainly occurs as euhedral–subhedral grains formed in the Stage I. Py2 within quartz veins from Stage II shows oscillatory zoning and can be distinguished into two subtypes by their distinct textures (Py2a and Py2b). Py3 coexisting with native gold, chalcopyrite, sphalerite, and galena is characterized by sulfide and silicate inclusions and is divided into two subtypes (Py3a and Py3b). The porosity and heterogeneous textures of Au-bearing pyrite indicate a process of dissolution and reprecipitation. The replacement was likely the result of dissolution–reprecipitation. However, Py1 has very low lattice-bound gold contents, indicating that obtaining high-grade gold orebodies through remobilization of lattice-bound gold is unreasonable. We suggest that the deposition of abundant native gold was induced by a new volume of Au-rich ore-forming fluids and triggered by extensive fluid phase separation during Stage II and Stage III. The δ34S values for the sulfides are similar, ranging from +0.9 ‰ to +5.8 ‰, and the lead isotope compositions of Stage II and Stage III sulfides are consistent. Fluid inclusions extracted from gold-bearing pyrite have elevated 3He/4He ratios (0.18–1.13 Ra) and 40Ar/36Ar (329.5–848.5), indicating the presence of mantle-derived fluids in the ore system.

Calcite U-Pb, pyrite Re-Os geochronological and fluid inclusion and H-O isotope studies of the Dafang gold deposit, South China

The Dafang gold deposit is one of the representative gold mineralization in southern Hunan province, South China. The gold orebodies mainly occur in the contact zones between late Jurassic granodiorite porphyry and late Paleozoic limestone as well as the fractures in them. Three primary mineralizing stages have been identified: pyrite + arsenopyrite ± chalcopyrite + quartz (stage I), pyrite + gold + calaverite + polymetallic sulfides + quartz (stage II), and pyrite + arsenopyrite + quartz + calcite (stage III). Pyrite samples separated from stage II yielded a Re-Os isochron age of 149 ± 16 Ma. Calcite samples from stage III demonstrated a U-Pb age of 157.7 ± 6.5 Ma. The above ages are similar to the zircon U-Pb ages of the local granodiorite porphyry although field evidences did not support a genetic link between them. The newly obtained mineralizing ages for Dafang indicate that this deposit is most likely related to deep or nearly late Jurassic intrusions (e.g., the Baoshan porphyry intrusion) and that this gold mineralization is synchronous with the large-scale W-Sn mineralization (160–150 Ma) for the Nanling Range in South China. The measured δDH2O (−103.5 to −81.4 ‰) and calculated δ18OH2O (−4.1 to + 4.9 ‰) isotope compositions for different stage vein quartz suggest that the Dafang ore-forming fluids were initially dominated by magmatic water, and were diluted by meteoric water in the late stage. Fluid inclusion studies indicate that the ore fluids belong to the H2O-NaCl-CO2-CH4 system, which cooled during its evolution (e.g., 230–337 °C, 150–246 °C, and 91–178 °C for stages I to III, respectively) with varied fluid salinity (4.7–9.2, 4.7–23.3, and 2.1–9.9 wt% NaCl eqv. for stages I to III, respectively). Fluid inclusions assemblages with different vapor and liquid phase ratios in a single quartz growth, and their similar homogenization temperatures with varying fluid salinities supported the fact that fluid boiling occurred in ore stage II. Combined with geological occurrences and the results from this study, we propose that gold was mainly transported in a reducing condition, and fluid boiling and host-rock sulfidation are the key factors for gold deposition at Dafang.

Deep exploration of Jiaodong type gold deposit, taking Shanhou gold deposit, southern part of Zhaoping fault as an example

Crustal response induced by the subduction of Paleo-Pacific Plate, is crucial to study the metallogenic law and prediction of Jiaodong type gold deposit. Gold deposits are preferentially hosted in the lithospheric-scale second-order faults, which provide migration channels, mineralization corridors, and the physicochemical conditions. Super-large gold deposits in northwestern Jiaobei Terrane are generally controlled by regional linear faults, such as Sansandao, Jiaojia, Zhaoping and Qixia faults. However, Zhaoping fault is exposed sporadically (in Xiadian and Jiangjiayao gold deposits) beneath a thick cover of Quaternary basalts, which indicating that limited information can be obtained by traditional geological survey. In this study, high-precision geophysical surveys such as gravity and controlled source audio frequency magnetotellurics (CSAMT) are conducted in the Shanhou gold deposit, which hosted in southern part of Zhaoping fault. Three integrated geophysical profiles results further identified the spatial distribution of second-order oblique-slip faults of Zhaoping fault and established the relationships between brittle deformation and mineralization. The spatial variability of stratum (high density 2.82 g/cm3 and intermediate to high specific resistivity 4000 Ω m), brittle-slip faults (intermediate density 2.73 g/cm3 and low specific resistivity 200 Ω m) and magmatite (low density 2.57 g/cm3 high specific resistivity 8000 Ω m) are identified by two inversion techniques, including the man-machine interactive inversion technology and nonlinear conjugate gradient technology. In addition, the geophysical inversion pseudo sections delicately portray a smooth-out waveform low specific resistivity anomaly, which strongly couples with the spatial ore-hosted locations and enrichment places. The gold mineralized alteration zones generally dips to southeast and the angle changing from 45° to 30°, which are strong coupling with the large-scale acid magmatic intrusion and extensional tectonics occurred in the late Mesozoic. Finally, according to the deep prospecting prediction, a gold ore body with 10 m in thickness was revealed by drilling below the depth of 1,015 m, which is hosting in the brittle deformation of Zhaoping fracture zone.

Fluid inclusion and in situ sulfur isotope studies of the carbonaceous strata-hosted Eryiling gold deposit in the Beishan orogen, NW China

The Eryiling gold deposit in the Jinwozi orefield is a carbonaceous strata-hosted gold deposit in the Beishan Orogen, NW China. The gold orebodies are mainly layered, lenticular, and vein hosted in Jinwozi Formation, different from the Jinwozi gold deposit. In this contribution, based on a comprehensive study including field investigation of ore geology, fluid inclusion microthermometry, and in situ sulfur isotopic composition, we discuss the origin and source of the ore fluids and the gold precipitation mechanism at the Eryiling deposit. The ore-forming process includes the early milky white quartz-pyrite vein, the main stage smokey gray quartz-sulfide vein, and the late-stage quartz-calcite vein. The auriferous vein characterizes the main-stage veins. By micro-thermometry, CO2-bearing(C-), Pure CO2(PC-), Water(W), and daughter crystal(S) types of fluid inclusions were identified and investigated. The early-stage quartz vein contains C-type FIs with a salinity of 3.5 to 7.7 wt% NaCl eqv., and total homogenization temperature (Th) of 243 and 321 °C. It shows that the ore fluids possess characters of low salinity, CO2-rich, and mesothermal. These characters resemble to those of orogenic-type gold deposits. The C-type FIs in the main stage quartz show salinity of 3.5 to 8.9 wt% NaCl eqv., and Th of 200 and 350 °C. The W-type FIs are coexisting with C-type FIs which they yield salinity of 5.5 to 10.2 wt% NaCl eqv., and Th of 158 – 287 °C. A large amount of immiscibility fluid inclusion assemblages found in the main stage quartz provide clear evidence for gold precipitation caused by fluid immiscibility. Trapping pressures of 61–233 MPa for the early stage and 48–182 MPa for the main stage are estimated, equivalent to mineralization depths of ∼ 8.1 km and ∼ 6.4 km, respectively. The δ34S value of sulfide increased from early-stage (average of 3.8 ‰) to main-stage (average of 6.4 ‰), indicating sulfur contributed by the wall rocks through fluid-rock interaction as the wall-rock sulfide display value of average of 16.2 ‰. In summary, the Eryiling gold deposit is situated in the altered carbonaceous rock of the Jinwozi Formation and regulated by a fractured zone, which could be considered a typical carbonaceous strata-bound orogenic gold deposit. Moreover, the similarity of ore-forming fluids between Jinwozi and Eryiling gold deposits indicates that they are the products of the same ore-forming fluid in different wall rocks.

Seismic Reflection Profiles Reveal the Ore-Controlling Structures of Carlin-Style Gold Deposits in Lannigou Gold Fields, Southwestern Guizhou, China

AbstractThe Carlin-style Lannigou gold deposit is hosted in Triassic flysch in the Nanpanjiang basin in southwestern Guizhou Province, southern China. This study is the first to use seismic exploration data to elucidate the structural architecture of the Lannigou Carlin-style gold deposit. We use regional seismic reflection data to show that gold orebodies are controlled by faults that link with the regional Lannigou-Weihuai fault, and we use this new insight to determine the relationship between mineralization and inverted basin faults to constrain the structural controls of this gold system.A grid of seven seismic sections covering the Lannigou gold fields is combined with field geologic data to reveal two distinct structural patterns. Seismic data reveals that the inverted, E-dipping Lannigou-Weihuai fault is shallowly penetrating (less than 2 km) in the north and increasingly penetrates the pre-Devonian basement rocks to the south, where the fault can be imaged to depths greater than 5 to 7 km. Basement-penetrating faults link the metamorphic basement and overlying basin successions that include potential source rocks for oil generation, interpreted gas reservoirs, and gold deposits. Therefore, these deep-seated faults are important channels for the migration of ore fluids, especially for the transport of hydrocarbon gas, which may have served as an important chemical trap for gold mineralization.Seismic data also reveals the W-dipping Qiaoluo fault that bounds the inverted Qiaoluo half-graben. Fault crosscutting relationships reveal an extensional episode from the Late Paleozoic to the early Anisian age of the Middle Triassic epoch (i.e., the depositional age of the second member of the Middle Triassic Xuman Formation), which is overprinted by an episode of middle Anisian basin inversion during deposition of the third member of the Xuman Formation. This inversion occurred at ca. 248 to 246 Ma. Based on the ore-controlling constraints and previous geochronological data, we consider that the Lannigou gold deposit was formed in the Late Triassic to Early Jurassic during syndepositional inversion of existing basement-penetrating basinal faults in a foreland basin. The first-order faults in the above structural belts, such as the Lannigou-Weihuai fault and the blind Qiaoluo fault, are most favorable targets for further exploration of undiscovered gold orebodies. This study demonstrates that seismic reflection is a powerful tool to reveal deep structures at varying scales from mineral deposits to sedimentary basins.

Ore Genesis of the Toudaochuan Gold Deposit in Central Jilin Province, NE China: Constraints from Fluid Inclusions and C–H–O–S–Pb Isotopes

The Toudaochuan gold deposit is a recently discovered lode gold deposit in Central Jilin Province. Gold ore bodies are dominantly controlled by NE-trending fault. The major hydrothermal period can be further divided into the quartz–pyrite stage (stage I), quartz–gold–polymetallic sulfides stage (stage II, major gold mineralization stage), and quartz–carbonate stage (stage III). Primary fluid inclusions (FIs) identified in quartz at different hydrothermal stages include liquid-rich aqueous FIs (L-type), CO2 FIs (C-type, including CO2-bearing C1-type FIs and CO2-rich C2-type FIs), and minor vapor-rich aqueous FIs (V-type). Microthermometry studies on different fluid inclusions indicate that the original ore-forming fluids belonged to the CO2–H2O–NaCl system characterized by a moderate–low temperature and low salinity in stages I and II, and they finally evolved into a H2O–NaCl system characterized by low temperature and low salinity in stage III. Fluid immiscibility is considered to be the key ore-forming mechanism. The initial ore-forming fluid was originated from magmatic water and was mixed with meteoric water in the later stage. The S and Pb isotope data suggest that the ore metal materials were derived from the mixed source of mantle and crust. Based on all the above data, therefore, it can be proposed that the Toudaochuan gold deposit is a mesothermal magmatic–hydrothermal gold deposit.

Principles governing the selection of ore regions for gold deposit search

Background. In 2020, the Auditing Chamber of the Russian Federation, based on a representative report by its expert analysts M. Men’ and A. Kaulbars, proposed expanding the search for deposits of a number of metals, including gold. Since the fund of easily discovered gold deposits coming to the surface has been significantly reduced, prospecting of ore regions most promising in terms of gold deposits becomes highly relevant.Aim. In connection with the above task, it seems expedient to outline territories within the currently known gold provinces, where the prerequisites and signs of gold ores could be detected with minimal expenditures for their subsequent verification by drilling.Materials and methods. The study involved calculating the shares of the world’s gold reserves attributable to each type of distinguished deposits located in various rocks. The extensive experience of prospecting work carried out in recent decades and culminated in the discovery of the Muruntau deposit in Uzbekistan, a world leader in the development of gold deposits, and Russian largest and giant deposits – Natalka, Sukholozhskoe, Nezhdaninsky, Degdekansky, Maisky, Oktyabrsky, Pavlik, Kupol, as well as the Bakyrchik deposit in Kazakhstan and others, clearly shows that the most promising and largest deposits are selectively localized in favourable rocks and largescale disjunctive dislocations, or faults. To identify favourable rocks, the distribution of the world’s gold reserves in various rocks was analysed, as well as the distribution of reserves in the areas of the largest deposits in ore-bearing faults as the most favourable fault types containing the most powerful and extended gold ore bodies.Results. A comparison of the shares of reserves has shown that the most promising for prospecting are those rock complexes containing the highest proportions of the world’s gold reserves. The article presents the distribution of shares of the world’s gold reserves for near surface and deep-formed deposits of various types. The main share of the world’s gold reserves in deeply formed deposits is shown to be concentrated in the Phanerozoic strata of sandy-clayey composition and in the interlayers of easily replaceable carbonate and amphibolite shales developed in the Proterozoic quartzite-phyllite rocks. The reserves of near-surface gold-silver and gold-telluride ores are selectively located in the young Mesozoic-Cenozoic volcanic rocks of basalt-andesite composition, accompanied by dikes, subvolcanic stocks and the pipes of explosive breccias with large-scale gold ore bodies confined to them. Thus, the most promising areas for prospecting new deposits are those composed of the mentioned rock complexes and crossed by ore-bearing faults, in the zones of which the main largest ore bodies are concentrated. Conclusion. The conducted study into the distribution of the world’s gold reserves in the deposits of various types, as well as the selective localization of ores in deposits with the main and large scale ore bodies in the zones of ore-bearing faults (and, accordingly, containing the concentration of the main share of reserves in a particular deposit), provides a basis for discovering new deposits of the precious metal with minimal expenditures, thus contributing to increasing the resource base of the Russian Federation.

Heterogeneity of mineral chemistry and sulfur isotopic composition of alunite in the Mankayan lithocap, northern Luzon, Philippines

The lithocap at Mankayan is a contiguous zone of alunite + quartz + pyrite that occur as pervasive alteration of the metavolcanic basement and dacitic pyroclastic rocks. Alunite + quartz + pyrite assemblage also occurs within hydrothermal gold-bearing veins and breccias. Several high-sulfidation epithermal gold orebodies have been previously delineated in the Lepanto Main Enargite orebody, and in the Northwest, Carmen, Florence West and Florence East quartz-pyrite-gold (QPG) veins. This study presents new data of mineral composition and sulfur isotopic ratios of alunites from different zones of the lithocap at Mankayan. Elemental composition maps and point analysis of alunites indicate compositional heterogeneity within a single alunite crystal. Common substituents to the K+ site are Na+ and H3O+, with few Ca2+ substitution in some sites. Limited occurrences of PO43- substitution to SO42- were also documented. Sulfur isotopic ratios (δ34SCDT) of alunite range from + 13 ‰ to + 24 ‰, which are typical of hypogene alunite. Sulfur isotopic ratios of coexisting pyrite are mostly negative, ranging from −5.4 to −1.0 ‰. Few samples of alunite from the Northwest and Florence West quartz-pyrite-gold veins have sulfur isotopic ratios similar to the values of its coexisting pyrite. The estimated temperature of formation using sulfur isotope geothermometry of alunite-pyrite pairs ranges from 197 °C to 364 °C, with most of the samples varying within 220 to 270 °C. The calculated bulk δ34S of the hydrothermal fluid was found to be + 5 to + 6 ‰ for the different mineralization events in Mankayan.The alunite crystals are heterogeneous even in the microscopic scale. Compositional maps show that K and Na concentration vary within single crystals, as well as among different crystals of a sample. The variations of K and Na content mostly follow the crystal growth structure, however, some alunite crystals with irregular variations are also present. Some samples contain aluminum-phosphate-sulfate (APS) minerals intergrown with alunite. Electron probe microanalysis of the alunite crystals showed a generally wide range of composition between the alunite – natroalunite solid solution.Using thermodynamic functions, a relationship between temperature and K+/Na+ of the hydrothermal fluids was determined across the range of alunite-natroalunite solid solution system. The model curves suggest that at temperatures less than ∼ 250 °C a slight change in fluid composition and/or temperature can vary the number of Na atoms per formula unit by 0.3 units. At higher temperatures, a more significant change in the physicochemical conditions is required for a substitution to occur. This explains the wide range of Na content in the alunites from the different parts of the lithocap.The characteristics compiled in this study reflect the fluctuations in temperature and fluid compositions that occurred during the multiple hydrothermal events in the Mankayan District.