Magmatic-hydrothermal Deposits Research Articles

Geological and mining heritages in the Seridó UNESCO Global Geopark: Ediacaran to Cambrian mineral deposits revealed by historical mines in Northeast Brazil

The coexistence of mining, geoparks, and conservation is an ongoing discussion for the implementation and development of UNESCO Global Geoparks (UGGps). The Seridó UGGp provides a classic example where mining plays a fundamental role in unveiling geological heritage, showcasing positive relationships between mining and the establishment of sustainable territories based on geoconservation. The aim of this paper is to investigate, within two geosites of the Seridó UGGp – Mina Brejuí and Açude Boqueirão – how geological heritage has been showcased in active mines, correlated with cultural mining heritage, and utilized in geotourism and geoeducation. The paper utilizes adapted geological heritage inventories and valuing techniques, integrating cultural aspects of the mining landscape to provide detailed insights into the complex areas of the geosites. Both geosites have been the sites of regionally significant Ediacaran-Cambrian magmatic-hydrothermal deposits since the early 20th Century, yielding metallic and non-metallic raw materials during the World Wars up to the present days. The Mina Brejuí geosite boasts one of the best exposures of WMo skarn mineralization in South America within its underground galleries. Açude Boqueirão is a mining district with several types of quarries and mines, and its geoheritage is linked to the initial descriptions of the Borborema regional pegmatitic province with Cambrian TaNb, LiBe, gemstones, and ornamental deposits, and also for the rare deposit of blue tourmaline gemstone. Particularly, the Boqueirão site requires valorization interventions, as its rich mining heritage is threatened by the expansion of the energy sector and illegal artisanal mining. Active mining operations could present a plethora of opportunities that encompass the geopark's concepts of conservation, tourism, and education. Inventories of mining heritage in geoparks serve as alternative sources for geotouristic routes.

Apatite as a Record of Magmatic–Hydrothermal Evolution and Metallogenic Processes: The Case of the Hongshan Porphyry–Skarn Cu–Mo Deposit, SW China

Apatite, as a common accessory mineral found in magmatic–hydrothermal deposits, effectively yields geochemical insights that facilitate our understanding of the mineralization process. In this research, multiple generations of magmatic and hydrothermal apatite were observed in the Hongshan porphyry–skarn Cu–Mo deposit in the Yidun Terrane in SW China. The geochemical compositions of the apatite were studied using in situ laser ablation–inductively coupled plasma mass spectrometry and an electron probe microanalysis to understand the magmatic–hydrothermal processes leading to ore formation. The apatite (Ap1a) occurs as subhedral to euhedral inclusions hosted in the phenocrysts of the granite porphyry. The Ap1b occurs later than Ap1a in a fine-grained matrix that intersects the earlier phenocrysts. Increases in F/Cl, F/OH, and F/S and decreases in ΣREE and (La/Yb)N from Ap1a to Ap1b suggest the exsolution of a volatile-rich phase from the magma. The skarn hosts three types of hydrothermal apatite (Ap2a, Ap2b, and Ap3), marking the prograde, retrograde, and quartz–sulfide stages of mineralization, respectively. The elemental behaviors of hydrothermal apatite, including the changes in Cl, Eu, As, and REE, were utilized to reflect evolutions in salinity, pH, oxygen fugacity, and fluid compositions. The composition of Ap2a, which occurs as inclusions within garnet, indicates the presence of an early acidic magmatic fluid with high salinity and oxygen fugacity at the prograde skarn stage. The composition of Ap2b, formed by the coupled dissolution-reprecipitation of Ap2a, indicates the presence of a retrograde fluid that is characterized by lower salinity, higher pH, and a significant decrease in oxygen fugacity compared to the prograde fluid. The Ap3 coexists with quartz and sulfide minerals. Based on studies of Ap3, the fluids in the quartz–sulfide stage exhibit relatively reducing conditions, thereby accelerating the precipitation of copper and iron sulfides. This research highlights the potential of apatite geochemistry for tracing magmatic–hydrothermal evolution processes and identifying mineral exploration targets.

Polysomatic intergrowths between amphiboles and non-classical pyriboles in magnetite: smallest-scale features recording a protracted geological history

Abstract Non-classical pyriboles (NCPs) have tetrahedral silicate chains (Ibeam) of multiplicity higher than single (pyroxene) or double (amphibole) Ibeams and are known from amphiboles in altered mafic-ultramafic complexes. NCPs, their polysomatic sequences, and inherent chain-width disorder are petrogenetic tools for interpreting igneous and metamorphic processes. Magnetite, a refractory mineral that can trap and preserve NCPs is a major constituent of iron oxide-copper-gold (IOCG) deposits. We undertook a nanoscale study to show that NCPs and amphiboles are hosted within magnetite cores from the Jatobá Ni-bearing IOCG deposit, Carajás district, Brazil. Monoclinic amphiboles and NCPs form polysomatic intergrowths or occur as sparse inclusions along {111}magnetite. There are two chemical populations of amphiboles: Mg-Fe- and Ca-(Al)-amphiboles, the latter including Ce-bearing Mg-hornblende and (ferro)tschermakite. The occurrence contains one of the widest ranges of chain silicates ever recorded, from simple intergrowths of single to triple Ibeam zippers, including pyroxene slabs, to longer NCP polysomes up to 15-Ibeam chains. Clinojimthompsonite (Cjim) is observed for the first time within magnetite. Although no discrete polysomes could be defined, the NCP-amphibole intergrowths have composition between Mg-Fe amphiboles and Cjim based on Ibeam averages of 2.5-2.7. Relationships between increase in the number of C and A cations from amphibole (2-Ibeam) to n chain silicates (nIbeam) are formulated as nIbeam = T(2+n) = C(5+3n) = A(1+n), n=integer. Empirical models of crystal structures, validated by STEM simulation, are shown for 4- and 5-Ibeam chain silicates. Co-crystallization of double- and triple-chain silicate structures with rhythmic intergrowths as larger blocks along b is often accompanied by rhythmic Ca-Fe zonation along a, supporting primary NCP crystallization via self-patterning during amphibole growth within magnetite in a close-to-equilibrium system. Chain-width disorder is documented from defects including planar faults, derailments, jogs, and swells. Violations of zipper termination rules indicate primary growth rather than replacement. Amphibole-NCPs inclusions support a multi-stage evolution for Jatobá magnetite. They formed during the first cycle of magnetite growth within a mafic/ultramafic lithology that records synshearing events. Subsequent formation of calcic-amphiboles, including Ce-bearing species, indicate IOCG-related fluids at the onset of mineralization. (Ferro)tschermakite formed at ~7.5 kbar during shearing associated with main ore deposition. The multi-stage amphibole-NCPs generations in magnetite revealed by nanoscale study emphasize the interpretive value of magnetite for overprinting events in terranes with protracted geological histories. Analogous NCPs are likely to be abundant in magnetite from magmatic-hydrothermal deposits hosted by greenstone belts and altered mafic/ultramafic complexes. Likewise, discovery of Ce-rich hornblende provides new avenues to understand the early, alkali-calcic alteration stages of IOCG systems and models for REE incorporation into, and subsequent release from chain silicates.

Fluid-induced dissolution–reprecipitation of tungsten minerals in the Hongling deposit, South China

Tungsten is a critical metal that is predominantly found in magmatic-hydrothermal W-Sn deposits. However, the behavior and controlling factors of tungsten in highly evolved granitic systems are not yet well-known. In this study, we examined the integrated mineral textures and geochemistry of wolframite and scheelite from the Hongling tungsten deposit in the word-class Nanling W-Sn metallogenic belt, South China. Our results reveal that wolframite and scheelite from the muscovite granite of the highly evolved Reshui granite pluton can be classified into three generations formed through a process of coupled dissolution-reprecipitation. Wolframite with altered relict textures was formed during the early magmatic stage, while the two generations of scheelite (Sch-I and Sch-II) were formed during the magmatic-hydrothermal transitional stage. The formation of Sch-I, which exhibits a notable positive Eu anomaly, required the participation of external Ca-rich reduced fluids within the magmatic exsolved fluids from the highly evolved peraluminous pluton. The porous Sch-II occurs as marginal overgrowth or fracture-filling textures and exhibits a similar negative Eu anomaly as the dissolved wolframite. These three generations of tungsten minerals exhibit distinguishable REE contents and distribution patterns, with increasing LREE and decreasing HREE trends. The fluctuation of oxygen fugacity and the compositional evolution of tungsten minerals from wolframite through Sch-I to Sch-II indicate the involvement of external Ca-rich reduced fluids within the magmatic exsolved fluids from the highly evolved peraluminous pluton. The coupled dissolution of wolframite and the reprecipitation of scheelite were likely induced by intensive fluid-rock interactions, which are critical for the remobilization and enrichment of tungsten in magmatic-hydrothermal deposits. We inferred that such fluid-induced dissolution-reprecipitation of tungsten minerals provides new insights into the formation of the world-class Nanling W-Sn metallogenic belt in South China.

Genesis of Caoziwa Pb–Zn Deposit in Tengchong Block, SW China: Constraints from Sulfur Isotopic and Trace Elemental Compositions of Sulfides

The Caoziwa Pb–Zn deposit is one of the typical vein-type Pb–Zn deposits in the western part of the Tengchong block. Due to limited research, the genesis of these deposits is unknown. In this study, the sulfur isotopic and trace elemental compositions of sulfides from the Caoziwa Pb–Zn deposit were analyzed to trace the sources of ore-forming materials, and to reveal the genetic type of this deposit. The results show that abundant Co, Ni, As, and Se, and less Cu, Zn, Ag, Cd, Sn, Sb, Te, Pb, and Bi could enter pyrite by isomorphic substitution. Elemental Mn, Fe, Cd, Co, and Ni could substitute Zn to enter sphalerite, while the contents of Ag, Sn, and Sb are mainly controlled by the Pb-rich inclusions in sphalerite. Elemental Bi, Sb, Cd, Sn, Ag, and Tl mainly enter the galena grains via an isomorphic substitution mechanism of (Bi, Sb)3+ + (Cd, Sn)2+ + (Ag, Tl)+ ↔ 2Pb2+. Both sulfur isotopic compositions and trace elemental compositions indicate that the ore-forming materials and fluids of the Caoziwa Pb–Zn deposit mainly originate from magmatic hydrothermal fluid related to Paleocene granitic magmatism. Combined with the geological facts that some skarnizations developed in the northern part of the ore field near the Paleocene granite, the Caoziwa Pb–Zn deposit is suggested to be a magmatic hydrothermal vein-type deposit that probably belongs to a distal part of a skarn mineralization system developed by the intrusion of Paleocene granitic magmatism in the western part of the Tengchong block.

Genesis of the Wutuogou Ag-Pb-Zn deposit in the Eastern Kunlun Orogenic Belt, NW China: Constraints from calcite U-Pb geochronology, mineral chemistry, and in-situ sulfur isotopes

The Wutuogou Ag-Pb-Zn deposit, a newly discovered vein-type deposit, is located in the Eastern Kunlun Orogenic Belt (EKOB), northwestern China. The vein-type Ag-Pb-Zn ore bodies are hosted in Middle Triassic granodiorite and monzogranite and are characterized by high-grade Ag, Pb, and Zn (average Ag: 293 g/t, Pb: 3.00 %, Zn: 2.85 %). Three paragenetic stages have been recognized: quartz + pyrite (Py-1) + arsenopyrite (stage I), pyrite (Py-2) + sphalerite + chalcopyrite + tetrahedrite + quartz (substage II-1), galena + pyrargyrite + freibergite + freieslebenite + quartz + calcite (substage II-2), and quartz + calcite (stage III). Except for Ag-bearing minerals (pyrargyrite, freibergite, and freieslebenite), invisible silver is also present in pyrite (1.91–165 ppm), sphalerite (3.86–8806 ppm), and galena (up to 0.21 wt%). The calcite is closely associated with sulfides in substage II-2 and yields a U-Pb age of 210 ± 7 Ma (MSWD = 2.7), which represents the ore-forming age (lower limit). Py-1 displays higher As contents and lower Co contents than those of Py-2, indicating a decrease in temperature from stage I to stage II. In addition, the Fe/Zn mass ratios (0.025–0.075) of sphalerite estimate the fluid temperature for substage II-1 of 246–284 °C, whereas the Ag/(Ag + Cu) and Zn/(Zn + Fe) mole ratios of freibergite estimate the fluid temperature for substage II-2 of 140–270 °C, further indicating the decrease of temperature from stage I through substage II-1 to substage II-2. Mineral assemblages of pyrite-chalcopyrite-tetrahedrite in substage II-1 and Ag-sulfosalts in substage II-2 suggest a decrease in sulfur fugacity (fS2). Both the decrease in fS2 and cooling of the mineralizing fluids facilitate silver precipitation. The heterogeneous compositions of the freibergite and the Ag zonation in sphalerite (Sp-1) resulted from retrograde solid-state reactions that redistributed Ag through microscale exsolution. The δ34S values (+5.49 to +7.78 ‰) of the sulfides and the low Zn/Cd ratios (107–195) of sphalerite indicate a felsic magma source for the ore-forming materials. Therefore, we concluded that the Wutuogou Ag-Pb-Zn deposit corresponds to a medium- to low-temperature magmatic-hydrothermal deposit associated with Late Triassic magmatism in the Eastern Kunlun Orogenic Belt (EKOB).

Fluid provenance and genetic type of the Bubin Cu-Pb polymetallic deposit, Kohistan-Ladakh island arc, north Pakistan: Evidence from mineralogy, fluid inclusion and O-H-S-Pb isotopes

The Bubin Cu-Pb polymetallic deposit in Gilgit-Baltistan, Pakistan, is a well-known vein-type ore deposit located in the Kohitan-Ladakh island arc. Due to its significant economic importance as the most important deposit type in the Kohistan-Ladakh island arc, a comprehensive study on its ore genesis, fluids evolution, and genetic classification not only shed new light on our understanding the formation of such polymetallic deposit at a typical intra-oceanic arc, but also of help for the mineral exploration. Here, we present the results from electron probe micro-analyzer, fluid inclusions, Raman spectroscopy, and isotopic studies (O-H-S-Pb) to gain insights into the source of ore-forming fluids and materials, as well as the genetic-type and mechanism of ore precipitation for the Bubin deposit. The mineralization processes were divided into three main stages: Stage I (quartz-pyrite), Stage II (quartz-sulfide), and Stage III (quartz-carbonate). Stage II further comprised two sub-stages: IIa (quartz-chalcopyrite-magnetite) and IIb (quartz-galena-fahlore). The ore-forming fluids exhibited high to moderate temperatures (154–540 °C) and varying salinities (0.35–44.30 wt% NaCl) throughout the stages. Stage I fluids displayed critical behavior with high temperature and low salinity, and their isotopic signatures suggested a magmatic origin. Subsequently, the ore-forming fluids gradually evolved from primary magmatic origin to the mixing of meteoric water, as demonstrated by oxygen and hydrogen isotopic values (δ18Ofluid = -1.34 to 6.29 ‰, δD = -112.4 to −76.1 ‰). The δ34S values (-2.92 to 6.52 ‰) and Pb isotopic ratios (208Pb/204Pb = 39.06 to 40.93, 207Pb/204Pb = 15.72 to 15.99, and 206Pb/204Pb = 19.44 to 20.80) suggested a deep magmatic source for the ore-forming fluid, with metals primarily derived from the upper crust, likely associated with the Ladakh Batholith. Fluid boiling and maxing are the dominant mechanisms for ore mineral precipitation. Additionally, the high to moderate temperature and salinity, presence of solid-bearing and vapor rich inclusions, a Co/Ni ratio > 1, the Ni-As-Co diagram, and O-H-S-Pb isotopic evidence collectively support the classification of the Bubin Cu-Pb polymetallic deposit as an intrusion-related porphyry-style magmatic hydrothermal deposit.

Ab-initio calculations and molecular dynamics simulations of In, Ag, and Cu replacing Zn in sphalerite: Implications for critical metal mineralization

Sphalerite has been recognized as the most important carrier mineral of the critical metal of indium (In), which mainly exists in sphalerite lattice through isomorphous substitution for Zn. It is widely reported that there are two significant coupled substitution schemes, namely Ag++In3+→2Zn2+ and Cu++In3+→2Zn2+, for In entering sphalerite in natural mineralization. However, there is still little known about physicochemical constrains on these two substitution reaction processes, which hinders the understanding of In mineralization. Thus, the current study uses ab-initio calculations and molecular dynamics simulations to investigate the replacement processes of Zn by In, Ag and Cu in sphalerite. The doped systems of Zn30InAgS32 and Zn30InCuS32, which correspondingly represent the products of the two substitution processes, were constructed by using 2 × 2 × 2 supercell model of sphalerite. Molecular dynamics method was employed to simulate the doped models, obtaining average configurations and formation energies at different temperatures. Then, ab-initio calculations were utilized to study the population values and electronic properties of the simulated configurations. In order to simulate a system close to natural mineralization conditions, a constant pressure of 30 MPa was set in molecular dynamics simulations, as this pressure level can represent the average metallogenic pressure observed in magmatic-hydrothermal deposits associated with In-bearing sphalerite. The temperature parameters were tested within the range of 175 °C to 400 °C, covering the known possible ore-forming temperatures. The simulation results show: (1) it is more stable for In to enter sphalerite via the coupled substitution scheme of Cu++In3+→2Zn2+ than that of Ag++In3+→2Zn2+; (2) the favorable temperatures for the two substitution processes are 225–250 °C and 325–350 °C; and (3) the changes in chemical reactivity caused by temperature fluctuations during the substitution processes of Zn by In, Ag and Cu may lead to the cyclic oscillation distribution that is commonly observed for In within sphalerite in magmatic-hydrothermal mineralization systems. This discovery not only shows the physicochemical properties of In-rich sphalerite formed by the two reaction processes of replacement of Zn, but more importantly, provides deep insights into the natural mineralising process of In at the atomic or/and molecular scale.

Genesis of the Hatu gold deposit: Constrained by in situ S[sbnd]Pb isotope geochemistry of pyrite

As the largest gold deposit in west Junggar, the Hatu gold deposit is located between the Anqi and Hatu faults in the Hatu-Sartohay district. The orebodies, composed of gold-bearing quartz veins and auriferous altered wall-rocks, are controlled by NE-, NW-, and EW-trending faults in Early Carboniferous volcano-sedimentary rocks. In this study, integrated textural, in situ sulfur and lead isotope analyses of pyrite grains in the host rocks and ores reveal new information on the sources of the ore-forming fluids and metal, as well as the mechanism of gold deposition. Framboidal pyrite in tuffaceous siltstone has a large δ34S range of −26.7 to +54.0 ‰, which is attributed to sulfur-reducing bacterial (SRB) activity during sedimentary-diagenetic process. Fine-grained subhedral pyrite in meta-basalt shows negative δ34S values from −26.7 to −12.1 ‰, which may be generated by reduction of seawater sulfate by ferrous iron bearing minerals during metamorphism. The δ34S values of four generations of hydrothermal pyrite (Py1–Py4) in the orebodies vary in a narrow range from +1.4 to −1.9 ‰. The sulfur isotopic characteristics of the hydrothermal pyrite are similar to most magmatic hydrothermal deposits, but differ from the metamorphic pyrite in meta-basalt and the framboidal pyrite in tuffaceous siltstone. In addition, the uniform in situ lead isotope ratios of hydrothermal pyrite resemble the lead isotopic compositions of the granitic plutons in the west Junggar, but differ from those of pyrite in meta-basalt. The progressive decrease of δ34S values from early-stage pyrite (+0.7 ‰ to +1.4 ‰) to late-stage pyrite (−1.9 ‰ to +0.4 ‰) corresponds to the major gold precipitation processes, which can be explained by gradual decrease of oxygen fugacity and increase of pH with decrease of temperature of a gold-bearing magmatic-hydrothermal system. A relatively stable environment for Au precipitation probably is a key factor controlling the scale of gold deposit, as the ore-forming fluid has enough time to form large gold deposit such the Hatu gold deposit.

Crustal architecture and metallogeny associated with the Paleo-Tethys evolution in the Eastern Kunlun Orogenic Belt, Northern Tibetan Plateau

The Eastern Kunlun Orogenic Belt (EKOB) in the Northern Tibet Plateau hosts a wide variety of metal deposits related to the Late Paleozoic to Mesozoic magmatism. In this study, we investigate the spatio-temporal distribution of the Late Paleozoic to Mesozoic granitic rocks and associated metal deposits in the EKOB and provide a comprehensive compilation of the geochronological, geochemical and isotopic data on these rocks. We compute regional zircon Hf isotope and crustal thickness maps from the data, based on which a comprehensive model is proposed involving subduction (ca. 270–240 Ma), continental collision (ca. 240–224 Ma), and post-collisional extension (ca. 224–200 Ma) for the Late Paleozoic to Mesozoic Paleo-Tethys evolution in the EKOB.Zircon Hf isotopic and crustal thickness mapping of Late Paleozoic to Mesozoic magmatic rocks was carried out to evaluate their spatio-temporal and genetic links with the regional metallogeny. The polymetallic Fe-skarn and porphyry Cu (Mo) deposits in the EKOB are located above the Moho uplift region, featuring a comparatively thin crust. Granites associated with porphyry Cu (Mo) and polymetallic Fe skarn mineralization are commonly characterized by high εHf(t) and younger TDMc values, whereas granite related to Cu-Mo-Sn skarn deposits exhibit more variable εHf(t) values, TDMc ages, and the crust thickness, which suggest that more crustal materials contributed to the formation of Cu-Mo-Sn skarn deposits than those for porphyry Cu (Mo) and polymetallic Fe skarn mineralization. In contrast, vein-type Au deposits are located primarily where the Moho surface displays a depression, i.e., where the continental crust is relatively thick. The magmatic rocks associated with Au mineralization are characterized by low εHf(t) and high TDMc values, representing reworked ancient crustal components, similar to those associated with porphyry Mo and epithermal Ag-Pb-Zn-(Au) deposits. Our study indicates that the emplacement of magmatic-hydrothermal deposits was controlled by the crustal structure and magma sources.

The Chemical Composition of Helvine-Group Minerals and Implications for Ore Genesis: Case Studies from the Dawan, Qidushan, and Taoxikeng Deposits

Abstract Helvine-group minerals have characteristic chemical compositions and textures and occur in different environments within magmatic–hydrothermal deposits. However, their origin is still unclear. There are several quartz-vein beryllium deposits with different element assemblages existing in southeastern China; these include the Dawan Be-Mo, Qidushan Be-Zn-Sn, and Taoxikeng Be-W deposits. We present the chemical composition of helvine-group minerals analyzed by electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry, in addition to zircon sensitive high-mass-resolution ion microprobe U-Pb and cassiterite laser ablation inductively coupled plasma mass spectrometry U-Pb ages. The zircon and cassiterite U-Pb data indicate that the Qidushan deposit formed during the Late Cretaceous (127–132 Ma). The electron probe microanalysis data show that the helvine-group minerals from the three deposits are helvine and/or danalite. A wide variety of different trace elements display high concentrations in the different deposits [e.g., helvine-group minerals from the Dawan deposit are rich in Li, B, Sc, V, Ga, Y, Sn, Cs, Th, and U; those from the Qidushan deposit are rich in Sc, Cd, and Sn; whereas those from the Taoxikeng deposit are rich in Y, Cd, Sn, Ta, and total rare-earth elements (ΣREE). The material analyzed from the Dawan deposit has the highest concentrations of Li (28.03–134.96 ppm), Sn (126.01–709.24 ppm), Sc (108.10–287.64 ppm), Cs (0–37.24 ppm), Th (4.78–112.63 ppm), and U (0.79–4.13 ppm). The material analyzed from the Taoxikeng deposit has the highest concentrations of Y (594.95–899.95 ppm), Cd (22.63–25.21 ppm), Ta (0.41–0.86 ppm), and ΣREE (281.69–451.79 ppm). However, those from the Qidushan deposit have the lowest concentrations of Y (10.21–37.70 ppm), Sn (0–26.88 ppm), U (0–19.06 ppm), Eu (0–0.14 ppm), and Cs (being below the detection limit). All of them are rich in heavy REEs but poor in light REEs, with distinctive REE patterns. Our results reveal that both crystallographic substitution and fluid composition control the enrichment of trace elements in helvine-group minerals. The textures and trace element compositions of helvine-group minerals can represent various parageneses and ore-forming fluid compositions. We propose that the δEu values and (La/Yb)N ratios can be used as markers to discriminate the genesis of helvine-group mineral precipitated from different environments based on the chemical compositions and the origin of ore-forming fluids.

Genesis of the Yawan Sb deposit, West Qinling Orogen, Central China: Constraints from S–Pb–C–O isotopes and Sm[sbnd]Nd geochronology

The Yawan Sb deposit is a large deposit located in the Xihe County, Gansu, northwestern China. Ore bodies are hosted in the Triassic limestone and are controlled by the NE- trending faults, occurring as lamellar, lenticular, veined, and lentil. Based on the cutting relationship between veins and mineral assemblages, the ore-forming process can be divided into four stages: I) pyrite + stibnite + milky quartz stage, II) stibnite + pyrite + gray-black cryptocrystalline quartz stage, III) stibnite + calcite + fluorite stage, and IV) clear and colorless calcite stage. The δ34S values (−2.5 ‰ to 5.8 ‰) of sulfides from stage II are similar to those associated with magmatic systems, but significantly different from the values (δ34S = −12.8 ‰ to 18.8 ‰) of pyrites from strata, suggesting that magmatic sulfur was the source for S2− in stage II. The δ34S values (−9.5 ‰ to −7.5 ‰) of stibnites from stage III are depleted in 34S relative to those of stage II, probably due to the increasingly mixing of meteoric water and SO42− from the strata. The Pb isotopes of sulfides from stage II and III (206Pb/204Pb = 17.745–19.176, 207Pb/204Pb = 15.478–15.711, 208Pb/204Pb = 37.7–38.742) show a mixed source of crust and mantle. The δ13C and δ18O values of calcites range from −0.84 ‰ to 3.94 ‰ and from 4.74 ‰ to 13.24 ‰, respectively, indicating that the ore-forming fluids originated from magmatic water, but influenced by water-rock interaction and meteoric water in the late stage. The SmNd isochron age of five calcite simples from stage III is 199.9 ± 1.7 Ma (MSWD = 1.6) with initial εNd values of −8.4, indicating that Yawan Sb deposit formed in the Late Triassic to Early Jurassic. On the basis of the data obtained in this paper, we consider that the Yawan Sb deposit is a distal magmatic-hydrothermal deposit formed during the transitional tectonic regime from the syn-collision to post-collision. Combined with previous studies, future exploration should focus on the distal magmatic-hydrothermal Sb deposits controlled by faults around concealed granites, and skarn-type deposits also need attention in Yawan-Daqiao district.

Genesis of the Questa Mo Porphyry Deposit and Nearby Polymetallic Mineralization, New Mexico, USA

Abstract The Oligocene Latir magmatic center in northern New Mexico is an exceptionally well exposed volcano-plutonic complex that hosts a variety of magmatic-hydrothermal deposits, ranging from relatively deep, F-rich porphyry Mo mineralization to shallower epithermal deposits. We present new whole-rock chemical and isotopic data for plutonic rocks from the Latir magmatic center, including extensive sampling of drill core samples of intrusive rocks from the Questa porphyry Mo deposit. These data document temporal chemical trends of porphyry-related mineralization that occurred after caldera-forming magmatism and during postcaldera batholith assembly. Silicic magmas were generated multiple times throughout the history of the Latir magmatic center, but few are associated with the formation of a mineral deposit. Whole-rock trace element ratios and Sr, Nd, and Pb isotope compositions vary throughout the protracted history of silicic magmatism. The caldera-forming ignimbrite and early phase of postcaldera intrusions are unmineralized, more enriched in high field strength elements, and generally contain less radiogenic Sr and Pb and more radiogenic Nd than later intrusions. The Questa porphyry Mo deposit formed immediately after the most isotopically primitive phase of the batholith was assembled, ruling out simple reworking of juvenile mantle-derived crust as the source for mineralizing magmas. Rhyolite dikes associated with polymetallic sulfide deposits intruded ~800 k.y. after Mo mineralization, and Nd isotope data indicate that these dikes are associated with different batches of magma and are unrelated to the Mo-mineralizing intrusions at the Questa mine. Together, these data indicate that the source of magmas changed significantly throughout the 10-m.y. history of the magmatic center. We assess multiple genetic models for porphyry-related magmatism against this data set, favoring models with discrete periods of magma genesis from a deep hybridized zone in the lower crust giving rise to the punctuated periods of mineralization. These observations suggest that the formation of mineral deposits within a central magmatic locus is likely the result of the piecemeal assembly of individual hydrothermal-magmatic systems, and that distal and younger polymetallic mineralization commonly observed near known porphyry deposits represents decoupled processes.

Texture and geochemistry of sphalerite from the Chitudian Pb-Zn-Ag deposit, southern margin of the North China Craton: Implications for the enrichments of Cd, Ga, and In

The Chitudian Pb-Zn-Ag deposit, located in the southern margin of the North China Craton (SNCC), is a typical magmatic-hydrothermal deposit, where sphalerite is the predominate ore mineral with significant concentrations of critical metals, including Ga, In, and Cd. However, previous studies paid little attention to the critical metals in the deposit. This study carried out in-suit elemental analysis on the sphalerite from the Chitudian deposit, aiming to constrain the spatial distribution and enrichment mechanism of critical metals. In the Chitudian deposit, five types of sphalerite were identified (Z-Sp, Y-Sp1, Y-Sp2, X-Sp1, and X-Sp2), which differ in color, texture, and chemical composition. The concentrations of Cd, Ga, and In of these sphalerites range from 1440 to 5145 ppm, 0.53 to 528 ppm, and 0.75 to 2113 ppm, respectively. In detail, Cd is mainly concentrated in the sphalerites from the hydrothermal vein-type orebodies relative to skarn-type orebodies. Indium is progressively depleted from granite-proximal locations to granite-distal locations, and the Fe-rich sphalerite is an excellent host of In. Gallium enrichment is only observed in the tectonically deformed location of the sulfide ore vein, where the Ga-rich sphalerite is poor in Fe and shows a complex texture. Microanalysis conducted on the Ga-rich sphalerite suggested that Ga, together with In, Sn, and Cu, are removed from the deformed sphalerite by mineral-fluid interaction and subsequently sequestered by the late sphalerite cement. Considering that the Ga-rich sphalerite is close to the Ga-bearing coal bed of the Meiyaogou Formation, it is likely that the coal bed could be a potential source for Ga. These results highlight that tectonic deformation followed by hydrothermal fluid overprinting is favorable for the enrichment of critical metals in sphalerite-rich deposits.

Strategies for Targeting in Undercover Terrains: Modeling Multi-Source Data in Apuí Region, SW Amazon Craton, Brazil

Exploring covered terrains is a challenge that requires the integration of multiple sources of knowledge, particularly in the initial stages of mineral exploration. The Apuí region, located in the Southwestern Amazon Craton, has a small and constant gold production, despite the deep cover and limited geological knowledge. The gold is mainly hosted in quartz veins and breccias that cut Paleoproterozoic volcano-sedimentary sequences. The occurrences have similar characteristics to magmatic–hydrothermal deposits, such as a lack of regional metamorphism and intense hydrothermalization. We undertook a multi-source prospective investigation on different scales using 2D and 3D techniques to translate the footprints of the mineral system into mappable criteria. Gold prospectivity maps for the Juma District and Guida Target were produced by integrating geological, geochemical, and geophysical datasets in knowledge-driven fuzzy systems. Regional airborne magnetization vector inversion (MVI) models were utilized. The correlation between the drill cores and the magnetic susceptibility models highlighted a potential surface for gold mineralization associated with the boundary between a granitic intrusion and volcano-sedimentary rocks. The prospectivity maps reduced the search area, and the regional susceptibility models allowed for the reconnaissance of structures and bodies that may be related to gold mineralization at depth. The results present new strategies for increasing discovery performance in the Southern Amazon Craton under cover.

Exhumation history of the Katebasu gold–copper deposit, Western Tianshan, NW China: Constraints from (U–Th)/He and fission-track thermochronology

Numerous Paleozoic deposits have been found in the Tianshan Mountains. Postmineralization burial plays an important role in the preservation of Paleozoic epizonal deposits. However, the preservation mechanisms for mesozonal deposits in the Tianshan Mountains need further investigation. The late Paleozoic Katebasu gold–copper deposit (with a reported mineralization age varying from ∼ 270 Ma to ∼ 330 Ma) in the Chinese Western Tianshan is a mesothermal magmatic hydrothermal deposit that formed at mesozonal depths. The exhumation process and preservation mechanisms of this deposit remain ambiguous. In this study, (U–Th)/He and fission-track dating were applied to samples from a vertical profile to constrain the exhumation history of the Katebasu deposit. Apatite (U–Th)/He and fission-track ages vary systematically with elevation, ranging from 32.4 ± 9.0 Ma to 176.4 ± 18.0 Ma and 106.4 ± 3.1 Ma to 181.7 ± 5.1 Ma, respectively. Zircon (U–Th)/He ages range from 220.4 ± 11.0 Ma to 260.1 ± 17.4 Ma. The age–elevation relationship and inverse thermal modeling reveal that the Katebasu deposit underwent two phases of exhumation. The first phase of exhumation, which caused at least 4 km of erosion, occurred during the late Paleozoic to Early Jurassic. The second exhumation started during the Early Oligocene, resulting in ∼ 0.9 km of erosion. A protracted period of tectonic stability during the middle–late Mesozoic to early Cenozoic and limited exhumation during the late Cenozoic uplift played important roles in the preservation of the Katebasu deposit.

Early Au-rich sulfide liquid saturation explains the low Au endowment of continental intraplate alkaline magmas

Abstract Alkaline magmatic systems formed in intraplate settings have a low Au endowment, contrasting with the high Au fertility of alkaline magmatic systems in arc and rift settings, which host numerous Au-rich porphyries and Cu-Au and Au-Ag epithermal deposits. Among other factors, the Au fertility of a magmatic system is determined by the Au concentration of the ore-forming magma, which is strongly controlled by the amount and chemistry of magmatic sulfides that fractionated during magma differentiation. To better explore the factors controlling the low Au endowment of alkaline magmatic systems formed in intraplate settings, we studied magmatic sulfide and silicate melt inclusions hosted in various phenocrysts from the Mont-Dore Massif (France). The magmatic system was saturated with Cu-poor, Au-rich sulfide liquid during its differentiation from basanite to trachyandesite, leading to a strong depletion of both Cu and Au in the residual melt. This presumably reduced the capacity of the magmatic system to form Au-rich magmatic-hydrothermal deposits. Such evolution contrasts with previous studies conducted in sulfide-saturated magmatic systems formed in arc settings, where an Au-poor monosulfide solid solution was the main sulfide phase to crystallize, only marginally affecting the Au budget of those systems. We conclude that the observed saturation of Au-rich sulfide liquid during evolution of the studied volcanic products could explain the low Au endowment of intraplate alkaline magmatic systems.

Metallogeny of the state of Oaxaca, southern Mexico: A review

The state of Oaxaca is one of the most geologically complex and diverse in Mexico. It comprises five tectonostratigraphic terranes of contrasting nature that form a sort of tectonic collage where several magmatic pulses were developed. The different lithological assemblages of Oaxaca favored the generation of a variety of ore deposit types, some of which have been a prime source of several commodities for centuries. This paper addresses the time-space relationship between ore deposits and tectono-magmatic events, based upon the available descriptions and radiometric ages. Most Meso-to Neoproterozoic ore deposits of Mexico occur in this region, and were formed during the regional granulite-facies metamorphic stage(s) recorded in the Oaxacan Complex. Such deposits are rare element-bearing pegmatites, nelsonites (ilmenite-apatite rich rocks), Ti-rich anorthosites, and pegmatites. The Oaxacan Complex also hosts a number of orogenic gold lodes that were likely formed in more than a single metamorphic episode and still require additional research to clarify their age and geological affiliation.The onset of arc-related magmatism in the Late Carboniferous-Permian is recorded by the intrusion of the calc-alkaline Zaniza, Cuanana and Honduras batholiths, along with several minor deformed and undeformed bodies enclosed in the Oaxacan Complex. Little is known about the metallogeny associated with such magmatism. Although supra-subduction magmatism re-initiated in the Jurassic and is probably responsible for the San Juan Mazatlán Cu porphyry, most of the metallogeny of Oaxaca is tightly linked to the Sierra Madre del Sur (SMS) igneous province, which began in Jalisco by the Late Cretaceous and migrated to the SE until it reached the Isthmus of Tehuantepec by the Middle Miocene. In Oaxaca, the Oligocene-Miocene coastal belt of granitic-granodioritic intrusions accounts for some IOCG deposits, especially in its easternmost portion, which then continues to the Coastal Chiapanecan Neogene batholithic belt.In W-NW Oaxaca, the intracontinental igneous province of the SMS marked the beginning of Cenozoic magmatism and is represented by thick volcanic-hypabyssal successions along with minor intrusions, with which copious magmatic-hydrothermal deposits are associated. Early Eocene and mid-Oligocene volcanism is restricted to the western half of the state, where basic-to intermediate-composition effusive products occur in the Mixteca and western Oaxaca tectonostratigraphic terranes. During this time span, many low-to intermediate-sulfidation epithermal, Fe-rich (IOCG) and polymetallic skarn deposits were produced. However, the “boom” in magmatic-hydrothermal mineralizations occurred during the terminal pulses of the SMS volcanism (Miocene), which comprise profuse intermediate volcanic rocks capped by the outburst of silicic magmatism. The early-to mid-Miocene event constitutes the most prominent in terms of metal endowment and diversity of ore deposit types, accounting for about 250 deposits and occurrences in the central and near-eastern portions of the state, which are ascribed to low-to intermediate-sulfidation epithermal, sulfide skarns, IOCG “clan” and Cu(–Mo) porphyry types. Among these, epithermal deposits are, by far, the most abundant type.Recent Ti-rich beach deposits and Au alluvial placers are present in southern and easternmost Oaxaca, respectively. In addition, supergene enrichment zones and uneconomic laterites occurrences are found in some localities.Oaxacan ore deposits can be grouped into five major metallogenic epochs: 1) Meso-Neoproterozoic REE-Th-U-Ti deposits and, possibly, orogenic gold lodes during the Olmecan-Zapotecan events (assembly of Rodinia); 2) feasible late Carboniferous-Permian (?) orogenic gold deposits; 3) early Eocene Ag–Au–Pb–Zn–Fe deposits during the onset of the SMS volcanic activity; 4) mid-Oligocene Ag–Pb–Zn–Sb–Hg–Fe(-Au) deposits during effusive-dominated pulses of the SMS volcanism; and 5) early-to mid-Miocene Au–Ag–Pb–Zn–Cu–Fe(-Mo-Sb) deposits during the termination of the SMS magmatism. The existence of a wealth of ore deposits with varying features underlines the economic potential of metallogenetic provinces and epochs in Oaxaca and exalts the necessity to expand the knowledge regarding the tectonic-magmatic-metallogenic evolution of the state.

Hydrothermal evolution and origin of the Suixian molybdenum deposit in the Tongbai orogenic belt, China: Constraints from geology, fluid inclusions and multiple isotopes (H[sbnd]O[sbnd]C[sbnd]S[sbnd]Pb)

The Suixian Mo deposit is a recently discovered deposit in the northern Hubei Province, Tongbai orogen. The Mo orebodies of this deposit are all hosted in the metamorphic rocks (leuco-gneiss, amphibolite and marble) of the Neoproterozoic Tianwangzhai Group, and these orebodies have no direct contact with the granite surrounding the host rocks. The mineralization types are dominated by disseminated ore and fine Mo-bearing quartz-sulfide veins. Hydrothermal alteration consists of abundant feldspathization, epidotization and chloritization, together with less garnetization, tremolitization, and muscovitization. A detailed study on fluid inclusions and multiple isotope (CHOSPb) analyses, together with geologic features, are carried out to investigate the fluid composition, fluid origin and evolution, the source of ore-forming materials, and the ore genetic type. In line with microthermometric measurements and laser Raman analysis on fluid inclusions from three hydrothermal stages, the ore-forming fluid in this deposit is characterized by medium–high temperatures and salinities, as well as richness in CO2 and CH4. Three hydrothermal stages are identified in this deposit, including (I) feldspar-quartz-amphibole-muscovite stage, (II) quartz-sulfides stage, and (III) quartz-calcite-scheelite-fluorite stage. From stages I, II to III, the temperatures change from 290 to 354 °C, through 229–312 °C, to 173–269 °C, with decreasing salinities of 12.6 to 16.3 wt% NaCl equiv., 4.5 to 13.4 wt% NaCl equiv., and 0.2 to 6.9 wt% NaCl equiv., respectively. Most of sulfur isotope data of sulfides (chalcopyrite, pyrite, pyrrhotite and molybdenite) show a narrow δ34S range from −2.0 to 3.0 ‰, suggesting a dominant magmatic source, but some data show either positive or negative values (δ34S: −13.3 to −10.6 ‰ and 9.8 to 11.2 ‰) which may indicate small contribution from the restricted wall rocks. The Pb isotope data (molybdenite, pyrite and pyrrhotite: 206Pb/204Pb: 17.239 to 18.483; 207Pb/204Pb: 15.378 to 15.717; 208Pb/204Pb: 37.889 to 38.850) imply that the lead of sulfides pertains to a mixture of magma (derived from the lower crust) and upper crustal materials (host metamorphic rocks). Based on evident CO2 and CH4 in fluid inclusions, the gradually depleted carbon isotopic compositions (δ13C: −5.4 to −9.9 ‰ at stage I, −14.8 to −19.7 ‰ at stage II, and −17.0 to −24.2 ‰ at stage III) and the HO isotope data, it is suggested that the ore-forming fluids were mainly magmatic fluids with mixture of some organic-containing water, and the thermochemical reaction between the fluids and organic matters (e.g., CH4) from host metamorphic rocks and fluid immiscibility are two important mechanisms for Mo mineralization. Compared with typical Mo deposits in the same orogen, the Suixian Mo deposit belongs to the magmatic hydrothermal vein-type deposit associated with intrusions rather than porphyry or skarn type deposit.

Ore Genesis of the Changkeng–Fuwan Au-Ag Deposit in Central Guangdong, South China: Evidence from Fluid Inclusions and C-H-O-S-Pb-He-Ar Isotopes

The Changkeng–Fuwan Au-Ag deposit is representative in South China, which is located in the southwest of the Qin–Hang metallogenic belt (QHMB). The Au and Ag orebodies are located in the same altered fracture zone, forming independent gold and silver orebodies respectively, with the characteristics of “upper gold and lower silver” in space. Three metallogenic stages have been identified: the pyrite–quartz–sericite stage, the polymetallic sulfide stage, and the quartz–calcite stage. The fluid inclusions (FIs) from the deposit are the two-phase liquid-rich (type I) and the pure liquid FIs (type II). The microthermometric measurements of type I FIs are characterized by temperatures of 158–282 °C and 146–289 °C and salinities of 0.35–9.88 wt.% NaCl equiv. and 0.18–11.70 wt.% NaCl equiv. The H, O, He, and Ar isotopic data show that the ore-forming fluids of the deposit were derived from a mixture of magmatic and meteoric fluids. The C and O isotopic data suggest that the carbon of the fluid may derive from a magmatic source. The S and Pb isotopic data indicate that the primary source of the metals in the Changkeng–Fuwan deposit may be a magma source. Based on the geological characteristics, FI microthermometry, and isotope data (C, H, O, He, Ar, S, and Pb), we propose that the Changkeng–Fuwan deposit should be classified as a far-source low-temperature magmatic–hydrothermal deposit.