Polymetallic District Research Articles

Mapping of Gold Prospectivity in the Qingchengzi Pb–Zn–Ag–Au Polymetallic District, China, with Ensemble Learning Algorithms

Mapping of Gold Prospectivity in the Qingchengzi Pb–Zn–Ag–Au Polymetallic District, China, with Ensemble Learning Algorithms

Unravelling the genetic relationship between pegmatites and granites in the Jiajika Li-Be polymetallic district, Songpan-Ganze Orogenic Belt, Southwestern China: Insights from monazite U-Pb geochronology and trace element geochemistry

The Jiajika Li-Be Polymetallic District is located in the Songpan-Ganze Orogenic Belt, Southwestern China. The Li-Be mineralization is genetically, temporally, and spatially, related to pegmatites in the Jiajika District. Hundreds of pegmatite dikes were emplaced surrounding the adjacent Majingzi granite pluton. Drill core samples from the 3,200 m deep Jiajika Scientific Drilling project (JSD-1) were acquired to determine the vertical extent and the petrogenesis and metallogeny of the granites, and the pegmatites, respectively, and to obtain a better understanding of their genetic relationship. The vertical zonation of the pegmatites from shallow to deep is as follows: shallow albite pegmatites; albite-microcline pegmatites; microcline pegmatites; and deeper more albite pegmatite. Spodumene occurs mainly in the shallow albite pegmatites (55–105 m depth), and disseminated beryl, columbite-tantalite, and cassiterite, mainly occur in pegmatites at depths less than 700 m. Eight samples were selected for monazite U-Pb geochronology and trace element geochemistry analyses from pegmatites and granites at different depths. LA-ICPMS monazite U-Pb geochronology for the pegmatites indicates two episodes of magmatic activity; one at 211–205 Ma (2σ, 523–2,494 m depth) and another at 193–192 Ma (2σ, 3,170–3,211 m depth). The crystallization age of the older pegmatites is in good agreement with the monazite U-Pb geochronology of the adjacent Majingzi granite (208–205 Ma, 2σ, 1,265–2,568 m depth) within analytical uncertainty, indicating their close temporal relationship. The younger albite pegmatite (193–192 Ma) is associated with the columbite-tantalite Nb-Ta rare-metal mineralization. Compared to those in the deep pegmatites (excluding the younger albite pegmatite in 3,170–3,211 m depth), and the adjacent granites, monazites in the shallow pegmatites and the adjacent granites are relatively enriched in Li, Th, and U, indicating the continuous evolution of a felsic magmatic system; with the residual melt more enriched in various incompatible rare-metal elements. Hence, the monazite U-Pb geochronology and trace element geochemistry indicate that a highly evolved felsic magma plays an important role in the petrogenesis of the Jiajika Li-Be pegmatites.

Trace Element and Sulfur Isotopic Analysis of Pyrite from the Luyuangou Gold Deposit, Xiong’ershan Au-Ag Polymetallic District, Central China: Implications for The Origin and Evolution of Ore-Forming Fluids

The Luyuangou gold deposit is located in the eastern section of the Xiong’ershan Au-Ag polymetallic district (XESPMD) and consists of a few gold-bearing veins found in the EW-striking faults located in the Archean Taihua and Mesoproterozoic Xiong’er Groups. The gold deposits contain numerous gold-bearing pyrites in thin quartz veins, representing an ideal tool for explaining the enigmatic genesis of gold deposits in the XESPMD. The distributions of trace elements and the sulfur isotopes of gold-bearing pyrite in the Luyuangou gold deposit were investigated to define the origin and evolution of ore-forming fluids. Five generations of pyrite have been identified: coarse-grained euhedral pyrite cores (Py1-1) and margins (Py1-2) in milky quartz veins, fine-grained pyrite (Py2) in quartz veins and host rocks, pyrite (Py3) in quartz + polymetallic sulfide veins, and pyrites (Py4) in quartz calcite veins. The distributions of trace elements indicated that Py2 and Py3 represented the main gold-bearing minerals and contained high concentrations of As, Au, Ag, Pb, Zn, and Cu, and the distributions were controlled by the micro/nanoinclusions. The δ34S values in the five pyrite generations ranged from −19.5 to 3.4‰. Py2 (−15.4 to −6.1‰) and Py3 (−19.5 to −12.4‰) had the lowest δ34S values, indicating that the sulfur originated from an oxidizing fluid. Py1 showed δ34S values (−0.3 to 1.9‰) corresponding to a magmatic origin. Py4 (1.1–3.4‰) displayed the highest δ34S values, indicating that the sulfur originated from the host rock under the action of meteoric water cycles. Analyses of the pyrite’s trace elements and sulfur isotopes, in combination with geological evidence, indicated that magmatic ore-forming fluids contributed to the formation of the Luyuangou gold deposit. The magmatic ore-forming fluids interacted with meteoric water during the main mineralization period. The changing physicochemical conditions of the mineralized fluids caused the precipitation of a large amount of gold and other mineralized elements.

Constraints on the genesis of the Laochang Pb–Zn ore, Gejiu district, Yunnan: Evidence from sulfide trace element and isotope geochemistry

The Laochang deposit is an important part of the Gejiu Sn–Cu polymetallic district, containing abundant reserves of tin, copper, lead, zinc and tungsten. The recently discovered sulfide Pb–Zn ore is located 1000 m underground in the Laochang deposit, and its genesis is not clear. In this study, the trace element concentrations and sulfur and lead isotope compositions of sulfides from the newly discovered Laochang Pb–Zn ore were analyzed to constrain mineralization conditions and genesis. Our results show that sphalerite from Laochang Pb-Zn ore contains high Fe, Cu, Ga, Ag, In and Sn, low Co, Ni, Ge and As and moderate Mn and Cd. Pyrite is enriched in Ag, Sb, Pb and As and poor in Co, Ni, Se, Ti and Mn. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) ablation profiles of sphalerite show that Fe, Cd, Mn, Ga, and In occur as solid solutions and/or lattice-bound ions, whereas Ag, Cu, Pb, Sb, and Sn are present in both mineral inclusions and solid solutions. Moreover, the profiles of pyrite indicate that Co, Ni and As enter the pyrite lattice by ion replacement and that Sn, Ag, Pb and Sb occur in both solid solutions and mineral inclusions.The Fe/Zn calculation temperature of sphalerites ranges from 299 °C to 344 °C (mean of 320 °C), while the sphalerite geothermometer (GGIMFis) temperatures range from 268 °C to 312 °C, with an average of 290 °C. These results indicate that the Laochang Pb–Zn ore formed under moderate- to high-temperature conditions. The sphalerites in the Laochang Pb–Zn ore is enriched in Ga and In, is poor in Ge, and has moderate contents of Cd which implies that it may be related to magmatic-hydrothermal fluid. Pyrites in this study have relatively low Co and Ni concentrations and low Co/Ni ratios, which also indicate magmatic-hydrothermal origin.The overall sulfur isotope compositions of sulfides from the Laochang Pb–Zn ore, ranging from −1.2 ‰ to +3.7 ‰, indicate that the S may be derived from the Laoka granite with some contribution from the wallrock. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of galena in the five samples range from 18.400 to 18.447, 15.656 to 15.697, and 38.478 to 38.968, respectively. These results imply that the ore-forming metals in the Pb–Zn ore were derived from the upper crust. Therefore, we believe that the Pb–Zn ore may be of magmatic-hydrothermal origin and represents the distal mineralization of the Laoka metallogenic system.

Origin of the Dongbulage Mo–Pb–Zn deposit in the Great Hinggan Range, northeast China: Geological, molybdenite Re–Os dating, fluid inclusion, and C–H–O–S–Pb isotope constraints

The Dongbulage porphyry Mo–Pb–Zn deposit is located in the Huanggang–Ganzhuermiao polymetallic district (HGD) in the southern part of the Great Hinggan Range in northeast China. The Dongbulage deposit is hosted by granite porphyry, and the wall rock alteration can be divided into quartz–potassic, quartz–sericite, and propylitic zones. The hydrothermal activity in the deposit can be divided into five stages, with molybdenite and Pb–Zn ore occurring mainly as veins and veinlets in stages II and III, respectively. The fluid inclusion (FI) types include liquid-rich (L-type), vapor-rich (V-type), and daughter mineral-bearing (S-type) FIs. Based on the combination of FI types and their temperatures and salinities, it is inferred that fluid boiling and incorporation of meteoric water were key factors in the precipitation of Mo and Pb–Zn, respectively. Hydrogen and O isotope data for quartz, and C and O isotope data for calcite indicate that the ore-forming fluids were primarily magmatic in origin, and were mixed with meteoric waters during their evolution. The S and Pb isotope data, along with the mineral paragenesis, suggest that molybdenite and chalcopyrite which precipitated during stage II were derived mainly from magmatic–hydrothermal fluids, whereas arsenopyrite, sphalerite, and pyrite that precipitated during stage III were strongly affected by the incorporation of surrounding strata materials. Rhenium–Os dating of molybdenite indicates that mineralization in the Dongbulage deposit occurred at 162.1 ± 1.3 Ma (n = 6; MSWD = 1.4). The results, combined with data from other deposits in the region of this age, indicate that important mineralization occurred in the HGD during 165–155 Ma.

Rapid Exploration Using pXRF Combined with Geological Connotation Method (GCM): A Case Study of the Nuocang Cu Polymetallic District, Tibet

The Nuocang Cu polymetallic district is located in western Gangdese, close to the south of the Luobadui–Milashan fault zone. A large number of metal deposits with the potential to be prospected, such as Chagele, Zhalong, Longgen, and Sangmola, have been found near this district. To further isolate the target prospecting area, we used a portable X-ray fluorescence spectrometer (pXRF) to conduct an in situ 1:10,000 soil pedogeochemical survey. The results show that the use of a pXRF combined with the geological connotation method (GCM) can accurately delineate the anomalies related to mineralization and highlight “weak” and “small” anomalies. It was also shown to effectively shorten the working cycle and ensure the continuity and timeliness of field work. Through sizing tests, the analysis of −10~+60 mesh soil samples achieved the best anomaly delineation effect. By studying the supra-ore, near-ore, sub-ore halo, and Th/U, the degree of denudation and the oxidation-reduction environment of the deposit were judged to be moderate. Ultimately, depending on the target area delineated by the pXRF, six Cu-Pb-Zn orebodies were uncapped by five exploratory trenches, which proved the potentiality of the Cu-Pb-Zn polymetallic epithermal deposit controlled by minor faults in Central Nuocang.

Trace elements in apatite from Gejiu Sn polymetallic district: Implications for petrogenesis, metallogenesis and exploration

The world-class Gejiu tin polymetallic district is located in southeastern Yunnan Province. Yet, the largest deposits are concentrated in the Masong and Laoka granites in the eastern area of Gejiu. To investigate the factors controlling Sn mineralization among intrusions in the Gejiu area, we collected apatite from eight different intrusions (including gabbro, monzonite, and granite) and determined the fertility indices of Sn deposits through the chemical composition of apatite. Analysis of the redox-sensitive elements in apatite showed that the ore-bearing granites have high Mn and low S content, high Y/∑REE and low La/Sm ratios, extreme negative Eu anomalies, and weak Ce positive anomalies compared to the barren intrusions, indicating that the formation environment of the ore-bearing granites was more reducing. The apatites in ore-bearing intrusions have lower Sr and higher Y contents, which suggests that these intrusions have a higher degree of fractionation than barren intrusions. The apatites in the Masong and Laoka granites have a high F content, which reflects the high F content of magma that contributed to the enrichment of Sn. The decreasing (Sm/Yb)N ratios with stable Sr content imply exsolution of Cl-rich fluids or crystallization of monazite and allanite. The exsolution of Cl-rich fluids can increase Sn solubility in the melt and promote the extraction of Cu from basalt. The apatites in the ore-bearing intrusions have high Li, Mn, Fe, and F contents and extremely low (Eu/Eu*)N ratios (<0.05). These results show that apatite can be used to distinguish Sn deposits from other deposit types and guide the Sn exploration.

Metal mobilization and precipitation in a Sn-W skarn system, Gejiu Sn district, China

In the Gejiu Sn-Cu polymetallic district, skarns with or without mineralization developed both at the contact zones between a granitic intrusion and carbonate-rich wall rocks and within carbonate-rich wall rocks. We analyzed the chemical and Sr, Nd, Pb, Li, and B isotopic compositions of mineralogically different zones in two hand specimens, i.e., a banded carbonate and a distal skarn with distinct reaction zones, to interpret chemical and isotopic variation in terms of (i) temporal compositional changes of skarn-forming fluids and (ii) reaction-induced exchange between fluids and carbonate wall rocks. The banded carbonates have seen little fluid-mediated exchange and therefore the compositions of the various bands reflect a two-component system of carbonates and detrital silicates. The compositional range of the banded carbonates represents the compositional heterogeneity of the protoliths of the distal skarn that experienced a pronounced impact by metasomatic fluids. The studied distal skarn is characterized by the vein-like aquifer (Zone I), reaction zones (Zone II and Zone III), and the carbonate aquitard (Zone IV). As evident from the distal skarn, the chemical and isotopic compositions of skarn-forming fluids change over time due to (i) processes in the fluid sources, (ii) variable contributions of different fluid sources, and (iii) reaction-induced exchange with the rocks bordering the aquifer, leading to selective addition or removal of elements from the fluid. During early interaction between aquifer fluids and its wall-rocks, the aquitard is partially consumed and the chemical and isotopic signature of the newly-formed minerals in the reaction zone represent a mixture of material derived from either fluids or wall rock. Once formed, the reaction zones largely protected the aquitard from further interaction with fluids. The Sr-budget of zones I to IV is dominated by Sr derived from the carbonate aquitard and redistributed during the consumption of older reaction zones. The Pb, Li, and B budgets of zones I to III are dominated by materials derived from the fluids. In contrast, the Nd isotopic compositions in zones II to III fall between the values of the carbonate aquitard and the aquifer. The ore elements occur in different zones, i.e., (i) scheelite, sphalerite, pyrite, and chalcopyrite precipitate in the aquifer and (ii) Sn substitutes in calc-silicates at the reaction front between zones II and III and is present in late fractures in Zone III. Thus, ore elements may have been transported by different skarn-forming fluids. The chemical and isotopic signatures of reaction zones do neither strictly reflect the nature of the reactive fluid nor reflect simple bulk mixing between fluid and wall rock, as (i) reaction-induced volume decrease may allow later fluids to infiltrate into earlier reaction zones, (ii) the fluid may be depleted in elements that have been scavenged from the fluid before, (iii) some elements having low compatibility in minerals of the reaction zones may have strongly partitioned into the fluid and are lost from the system. Although reaction zoning provides information about the nature of the reactive fluids, the mineralogically-controlled selective behavior of trace elements, i.e., most ore elements, does not allow to use the ore element content in skarn as a vector to mineralization.

A Stable Downward Continuation of Potential Field Data: A Case of Study of the Kalatag Polymetallic District, NW China

A Stable Downward Continuation of Potential Field Data: A Case of Study of the Kalatag Polymetallic District, NW China

Tourmaline composition and boron isotope signature as a tracer of magmatic-hydrothermal processes

Abstract This study presents a petrogeochemical and boron isotope study on tourmaline from the barren Damai, and the contemporaneous but ore-bearing Dewulu and Meiwu intrusions, to better understand the origins, sources, and fluid evolution of magmatic-hydrothermal ore systems and provide ore formation implications for gold, copper, and iron deposits in the Xiahe-Hezuo polymetallic district in the West Qinling, China. Tourmaline from all three intrusions shows similar compositions and encompasses Na-Fe schorl and Na-Mg dravite. Tourmaline at Dewulu is primarily found in tuffaceous breccias and a quartz diorite porphyry. In the tuffaceous breccia body, tourmaline occurs as fine-grained anhedral masses that fill voids and cement fragments of breccia and sickle quartz. Tourmalines in breccia are texturally similar to those formed in typical breccia pipes, which are attributed to explosion or collapse induced by a transition from magmatic to hydrothermal Si- and B-rich fluids. They display element substitutions controlled by Fe2+Mg–1, indicating a reduced environment. Values of δ11B are –6.6 to –4.0‰, representing the primary magmatic-hydrothermal fluids. Tourmaline from the Dewulu quartz diorite porphyry is coarse-grained, euhedral, and found in quartz-sulfide veins. The tourmaline displays oscillatory zoning textures but lacks correlative variations of major elements. The Fe2+Mg–1 and Fe3+Al–1 substitution mechanisms are dominant, demonstrating more oxidized fluids. The δ11B values in the cores, ranging from –7.1 to –5.6‰, suggest that the tourmalines in the quartz veins were inherited from magmatic-hydrothermal fluids that precipitated the fine-grained tourmaline in the tuffaceous breccia body. A large δ11B isotopic fractionation that decreases from cores (–5.6‰) to rims (–10.7‰) indicates significant fractionation during degassing occurred, increasing oxygen fugacity of the residual liquid. The Meiwu locality hosts fine-grained euhedral tourmalines coexisting with magnetite. Their composition is controlled by substitution between Al3+ by Fe3+ and has the lightest δ11B values ranging from –11.4 to –10.0‰. They are interpreted to result from skarn formation under oxidized conditions. In contrast, X☐Al(NaMg)–1 is the dominant substitution mechanism for Damai tourmalines and attributed to (geochemically) reduced fluids with a low salinity. We conclude that tourmalines with low Fe values, substitution mechanisms dominated by Fe3+Al–1, and large shifts of B isotopic composition are potentially an ore-forming indicator in the Xiahe-Hezuo polymetallic district.

Environmental assessment of heavy metal pollution in the polymetallic district of Kef Oum Teboul (El Kala, Northeast Algeria)

To the best of our knowledge, this study is the first to focus on the environmental assessment of heavy metals in the abandoned mining district of Kef Oum Teboul (KOT), which is located in the northeastern part of Algeria in an area classified by Ramsar as a Biosphere Reserve since 1990. KOT was one of the primary deposits of copper in the last century, and its releases are stored as dams that seriously threaten the environment. To assess the degree, distribution and sources of contamination approximately the mining area, liquid and solid samples were collected from the mining waste, the soils, and the stream sediment. The samples were analyzed to determine the pH, conductivity and contents of heavy metals (Pb, Zn, Cu, and Cd). The mining areas are characterized by high contents of heavy metals that exceed all norms, and the metal contents significantly decrease at significant low distances from these sources. According to the statistical methods used in this study (I-Geo, Pi, RI), the stream sediments and the soils are uncontaminated to moderately contaminated by Cu and Zn, moderately contaminated by Pb, and extremely contaminated by Cd.

Geochronology and geochemistry of the Yidi'nan quartz diorite in the West Qinling, China: Implications for evolution of the Palaeo‐Tethys Ocean

The Xiahe‐Hezuo polymetallic district, located the northwest portion of the West Qinling orogen, has a wide distribution of granitoid rock. Thus, information on the widespread Triassic granitoids in this area is important to constrain the tectono‐magmatic processes. However, the tectonic setting and genetic mechanism for the granitoids in this area are still controversial. In this study, we present a detailed description of zircon U–Pb ages, whole‐rock geochemistry, and Hf isotopes for the Yidi'nan quartz diorite and elucidate their petrogenesis and geodynamic implications. The quartz diorite was crystallized at 240.6 ± 1.8 Ma, based on its zircon U–Pb age. The quartz diorite belongs to the high‐K calc‐alkaline, metaluminous, I‐type granites and its fractionated REE patterns show enrichment of Rb, U, and Th, depletion of Ba, Sr, Nb, and Ta, and negative Eu. The zircons have negative εHf(t) values in a range of −7.66 to −2.72, corresponding to two‐stage model ages ranging from 1.66 to 1.48 Ga. The integrated data from petrology, geochronology, and bulk geochemistry suggest that the quartz diorite is formed along an active continental margin, and from the partial melting of the Lower Proterozoic crust. It is associated with the Palaeo‐Tethys oceanic crust that suffered northward subduction beneath the South Qinling Block from Permian to Early Triassic.

3D mineral exploration targeting with multi-dimensional geoscience datasets, Tongling Cu(-Au) District, China

The Tongling Cu(-Au) district is the most important magma-skarn type Cu(-Au) polymetallic districts in the Middle-Lower Yangtze metallogenic belt of China. The previous studies in the Tongling Cu(Au) district compiled available digital geological, geochemical, geophysical, and remote sensing datasets. As the discovery of near-surface Cu(-Au) deposits becomes more and more difficult in the Tongling Cu(-Au) district, we face the challenge of exploring for blind mineral deposits in the subsurface. Three-dimensional (3D) mineral potential mapping can provide effective exploration targeting by integrating multi-source and multi-dimension geoscience datasets. In this paper, firstly, a 3D district-scale geological model was constructed from multiple geoscience datasets. Secondly, multi-level (0 m, −300 m, −600 m, −900 m, −1200 m) exploration criteria were extracted by spatial analyses. Thirdly, the weights-of-evidence method, discrete smooth interpolation, and ordinary kriging interpolation were used to integrate multi-level exploration criteria including two-dimensional (2D) surface geochemical and remote sensing data into a 3D posterior-probability model. Finally, the concentration-area and concentration-volume fractal methods were used to define posterior-probability thresholds to outline 2D and 3D targets, respectively. The results indicated that the integrating performance of ordinary kriging interpolation is better than that of discrete smooth interpolation in 3D posterior-probability modeling. The whole procedure yielded a series of high-potential Cu(-Au) targets. The methodology discussed here can be used in other magma-skarn districts in the world.

Fluid inclusion and stable isotope (C, O and S) constraints on the genesis of the high-grade Langdu Cu skarn deposit in Yunnan, SW China

The Langdu Cu skarn deposit is the highest grade Cu deposit (average 6.49% Cu) in the Zhongdian polymetallic district in SW China. Skarns and ore bodies occur primarily in the contact zone of Upper Triassic Qugasi Formation (Fm.) and Late Triassic (ca. 217 Ma) intrusions. Disseminated, massive, stockwork, and vein-like sulfide ores occur in the skarn, quartz-calcite veins, porphyry and marble. Skarn minerals include pyroxene, garnet, actinolite, and epidote. Four types (six subtypes) of fluid inclusions (FIs) are identified in the sulfide-bearing quartz veins. Type-I liquid-rich two phase FIs have varying vapor/liquid ratios, and yielded homogenization temperatures of 110–338 °C and salinities of 1.7–29.5 wt% NaCl eqv. Type-II vapor-rich FIs contain CH4-N2 bubbles and homogenized to vapor at 262–425 °C. Type-III FIs are single phase at room temperature (20 °C). A vapor phase is present at below −120 °C, and the FIs homogenized at −117 to −114 °C. Type-IV daughter mineral-bearing FIs homogenized by halite disappearance at 295–392 °C, and have salinities of 37.8–46.6 wt% NaCl eqv. Such characteristics suggest that FIs were trapped by fluid immiscibility and phase separation. The δ34SCDT values of chalcopyrite and pyrrhotite are of −5.3 to 0.7‰. On the δ34S histogram, all Langdu data show a cluster of 32S-rich (δ34SCDT = −5.3 to −4.6‰) and a cluster of 34S-rich (δ34SCDT = −1.1 to 0.7‰). Type-I calcite (in skarn) and type-II calcite (in quartz-sulfide vein) have δ13CPDB and δ18OSMOW values of −8.4 to −7.8‰, −6.3 to −6.1‰ and 10.1 to 12.3‰ and 12.0 to 13.0‰, respectively. Type-III calcite from calcite-sulfide veins has δ13CPDB = −5.6 to 0.2‰ and δ18OSMOW = 12.5 to 16.3‰. Biotite, garnet and pyroxene, syn-ore quartz, and chlorite yielded δ18OSMOW values of 6.9‰, 4.1–5‰, 13.2–15.3‰, and 6.8‰, respectively. Sulfur, carbon and oxygen isotopic features of these hydrothermal minerals and the FIs microthermometric data suggest that the ore-forming fluids were magmatic sourced and contaminated by meteoric/formation water during ascent and/or fluid/wallrock interactions. Low δ34S (=−5.3 to −4.6‰) in sulfides and the CH4 in the FIs are interpreted to reflect the reaction between the magmatic fluids and the carbonaceous slate in Qugasi Fm. The methane likely expanded the vapor/liquid immiscibility field and reduced the sulfates (SO42−) to sulfides (S2−). And extensive water/rock reaction and fluid mixing may have occurred, leading to the high-grade Cu mineralization at Langdu.

Batholith-stock scale exploration targeting based on multi-source geological and geophysical datasets in the Luanchuan Mo polymetallic district, China

The Luanchuan Mo polymetallic district, which hosts world-class porphyry–skarn-type Mo (W) deposits, is located in the Qinling orogenic belt of the North China Craton. The mining depth of the porphyry–skarn-type Mo (W) deposit in the Luanchuan district is close to 550 m, and most exploration drillholes extend to more than 1000 m. The upper crustal architecture is important for understanding the geological setting and metallogenic model for mineral potential targeting on a district scale. In this study, subsurface intrusions and structures were defined using multi-level gravity data processing (i.e., bi-dimensional empirical mode decomposition) and geophysical inversion (including gravity, magnetotellurics, and controlled-source audio-frequency magnetotellurics). The results of our integrated geological and geophysical studies suggest that the Late Jurassic granite stocks are controlled by NE–NEE- and NW–NWW-striking faults. The porphyry–skarn-type Mo (W) deposits are distributed around the ore-controlling Late Jurassic granite stocks, which are connected to the granite batholith at depth. The volume of this batholith is about 96.96 km3. Based on geophysical interpretations and geochemical signatures of biotites from the granite stocks, the metallogenic potential of the granite stocks at Nannihu–Shangfanggou and Huangbeiling is considered to be greater than that of the granite stocks at Shibaogou–Yuku.

Paleo-tethys late triassic orogenic gold mineralization recorded by the Yidi’nan gold deposit, West Qinling, China

The Tongren-Xiahe-Hezuo polymetallic district in the West Qinling Orogen of central China has emerged as a promising new gold belt. However, significant debate exists as to whether the numerous Triassic intrusion-hosted lode gold deposits in the district represent intrusion-related or orogenic mineral systems. The Yidi’nan gold deposit is an example of a Triassic intrusion-hosted gold deposit endowed with an estimated resource of over 20 tonnes gold. The gold mineralization at Yidi’nan is fault-controlled and hosted by granite breccias associated with cataclastic zones. Its large size and intrusive host rocks make Yidi’nan an ideal site for attempting to resolve the origin of the intrusion-hosted gold systems in the West Qinling. Zircon U-Pb ages obtained as part of this study indicate that the ore-hosting quartz diorite pluton and a later dacite dike formed at 240.3 ± 2.5 and 239.3 ± 2.4 Ma. Hydrothermal sericite from fault gouge from main gold orebody returned much younger 40Ar/39Ar plateau and normal isochron ages of 220.21 ± 0.44 and 220.42 ± 7.69 Ma. Optical microscopy investigation revealed that the sericite coexists with gold-bearing sulfides, indicating that the sericite is coeval with gold mineralization. Our new age data reveal that gold mineralization at Yidi’nan postdated the Triassic magmatism by ca. 20 million years. Such a temporal framework is consistent with the observed geologic relationships, namely mineralized breccia ore crosscutting the quartz diorite host. Such evidence also suggests that the orogenic gold mineralization in West Qinling was not genetically linked to the Triassic magmatism associated with the subduction of the Paleo-Tethys Ocean. Instead, the formation of the Yidi’nan gold deposit appears to have been part of a mineralization event associated with a Late Triassic collisional event with the release of gold-bearing fluids possibly related to crustal thickening processes. High-angle reverse shear zones produced during ongoing continental collision probably facilitated the movement of hydrothermal fluids along major structures, eventually leading to the formation of plentiful orogenic gold deposits in West Qinling.

Genesis of the Shangjinshan W–Mo polymetallic deposit in the Eastern Jiangnan tungsten belt: Evidences from geochemistry, geochronology and zircon Hf isotope analyses

The newly discovered Shangjinshan W–Mo polymetallic deposit, located at the southern Anhui, southeast China, is a large-scale skarn-type tungsten polymetallic deposit. According to mineral assemblages, ore textures/structures and superposition relationships of the mineralization, three ore types have been recognized: veinlet-disseminated skarn (the primary type), quartz vein type and porphyry type. The mineralized event of this deposit could be divided into four stages: (I) the prograde skarn stage, (II) retrograde skarn stage, (III) quartz-sulfide vein stage, and (IV) quartz-calcite vein stage. The intrusion in the tungsten-rich district of the Shangjinshan is mainly composed of the granodiorite with zircon U–Pb ages of 138.4 ± 1.2 Ma to 136.7 ± 1.3 Ma. Meanwhile, Re–Os isotopic dating of five molybdenite samples yields an isochron age of 141.9 ± 3.1 Ma and a weighted average age of 139.3 ± 1.7 Ma, respectively. The ore-forming ages are consistent with the rock-forming ages within errors, indicating that the W-Mo mineralization is genetically related to the Shangjinshan granodiorite. The granodiorite is I-type granites, characterized by metaluminous to slightly peraluminous and high-K cal-alkaline compositions. They are also enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depleted in high field strength elements (HFSEs) and heavy rare earth element (HREEs), with obviously negative Eu anomalies (Eu/Eu* = 0.50–0.84). The zircon εHf (t) values and two-stage Hf model ages (TDM2) fall into the range −6.18 to −2.04 and 1.5–1.3 Ga, respectively. The relatively low rhenium contents in molybdenite and high radioactive Pb isotopes of the pyrites from stage II indicate that the ore-forming material was derived from Shangjinshan granitic magmatism. Together with previously published data, we propose that the W-related granitoids in the JNB were likely generated by partial melting of the Shangxi Group with some additional mantle materials. The granitic magmatism was caused by the asthenosphere upwelling, triggered by the roll-back of subduced Paleo-Pacific plate during Late Jurassic to Early Cretaceous. These granitic stocks predominately contributed to the production of skarn alteration and mineralization, resulting in the giant tungsten polymetallic district in the Jiangnan tungsten belt.

Petrogenesis of Ore-Hosting Diorite in the Zaorendao Gold Deposit at the Tongren-Xiahe-Hezuo Polymetallic District, West Qinling, China

The newly discovered Zaorendao gold deposit is in the Tongren-Xiahe-Hezuo polymetallic district in the westernmost West Qinling orogenic belt. The estimated pre-mining resource is approximately 13.6 t of Au at an average grade of 3.02 g/t. Mineralization is predominantly controlled by NW-trending and EW-trending faults within diorite intrusions and surrounding sedimentary rocks. In the present study, in situ zircon U–Pb geochronology and Lu–Hf isotopic analyses of the ore-hosting diorite at Zaorendao were measured using LA-ICP-MS. The data suggest that the diorite was emplaced at ca. 246.5 ± 1.9 Ma. The large variation of zircon Hf isotopic composition (ɛHf(t) values ranging from −12.0 to −1.8) indicates a two-stage model age (TDM2) that ranges from 1.4 Ga to 2.0 Ga. Such Lu–Hf isotopic compositions indicate that the diorite was dominantly derived from a Paleo- to Meso-Proterozoic continental crust. The wide range of εHf(t) and the presence of inherited zircon can be interpreted to suggest the mixing of Paleo- to Meso-Proterozoic continental crust with a mantle component. Combining such characteristics with the geochemistry of coeval rocks that are associated with the diorite, we therefore proposed that the gold-hosting Triassic diorite in the Zaorendao gold deposit formed in an active continental margin that was associated with the northward subduction of the paleo-Tethyan ocean.

New insights on the chronology of medieval mining activity in the small polymetallic district of Faravel (Massif des Écrins, Southern French Alps) derived from dendrochronological and archaeological approaches

A large amount of well-preserved timbers was found during several archaeological excavations of the Faravel mining site (Southern French Alps, between 1950- and 2150 m a.s.l.). 232 of these timbers were sampled for dendrochronological analysis and 67% of them were dated. These 156 larch (Larix decidua Mill.) series, crossdated against existing reference chronologies, were averaged for a site chronology spanning from 777 to 1243. From this dataset, 33 timbers with (almost) complete sapwood allowed us to obtain tree felling years with seasonal resolution. The chronological distribution of these felling years highlights nine distinct mining phases that occurred between 1059 and 1243, revealing a discontinuous exploitation of the study site during the medieval period. In addition, the presence of late wood in the vast majority of complete samples, demonstrates that logging mainly occurred during late fall and early winter. These results, combined with historical, palynological and archaeological investigations, plead for short, seasonal, and low-intensity, mining campaigns, mainly carried out after the bulk of agropastoral activities using rudimentary techniques with limited impact on the forest cover.

Genesis of tin-dominant polymetallic deposits in the Dachang district, South China: Insights from cassiterite U–Pb ages and trace element compositions

The Dachang tin-dominant polymetallic district in western South China, hosts a total reserve of 110 Mt ore @ 1% Sn, 3–5% by-products of Zn, Pb, Sb, In and Cu, and 100 to 300 g/t Ag. Economic tin orebodies in the district mainly developed in Devonian limestone, black shale and siliceous rocks, as massive/stratiform and vein/stockwork mineralization. LA-ICP-MS U–Pb dating on seven cassiterite samples from the Tongkeng-Changpo and Gaofeng Sn–Zn–Pb deposits, and the Dafulou, Huile and Kangma Sn–Zn deposits, yields weighted mean 206Pb/238U ages ranging from 90.3 ± 1.8 Ma to 95.4 ± 4.9 Ma. These dates are significantly younger than the Devonian ore-hosted strata, but agree well with the previously published zircon U–Pb ages of 96.6–93.9 Ma for the Longxianggai biotite granite within analytical uncertainties, showing a close temporal link between the granitic magmatism and tin mineralization.Cassiterite grains from various ore types in the Dachang district show clear growth zonations as reflected from their cathodoluminescence images. LA-ICP-MS trace element analyses of cassiterite grains indicate that they have relatively high Ti, Fe and W but low Nb and Ta contents, which corresponds to the clear luminescencing. Chemical variations of cassiterite from different ore types, i.e. cassiterite-sulfide ores and cassiterite-bearing quartz veins, are indistinguishable, except for more enriched Fe in cassiterite from cassiterite-quartz veins. Combined with Cretaceous U–Pb ages, elevated Fe and W contents of cassiterite suggest tin-dominant polymetallic deposits in the Dachang district were formed in a granite-related magmatic-hydrothermal system controlled by the Longxianggai biotite granite, precluding their syngenetic origin.