The Hongqiling is a vein-type Sn-W polymetallic deposit in southern Hunan (South China). It is geologically located on the northern margin of the Nanling metallogenic belt. Based on the mineral assemblage and vein crosscutting relationship, three mineralization stages were identified: Sn-W mineralization (S1: cassiterite, wolframite, scheelite, arsenopyrite, molybdenite, pyrite, chalcopyrite, and quartz), Pb-Zn mineralization (S2: chalcopyrite, pyrrhotite, galena, sphalerite, pyrite, quartz, and fluorite), and late mineralization (S3: quartz, fluorite, calcite, galena, sphalerite, and pyrite). According to laser Raman probe analysis, H2O dominates the fluid inclusions in the S1 and S2 stage quartz, with CO2 and trace N2 following close behind. The ore fluid has low salinity, low density, and a wide temperature range, as per our microthermometric data: the S1 stage has homogenization temperatures (Th) of 236–377.6 °C (average 305.3 °C) and salinity of 3.5–10.7 wt.% NaCleqv; the S2 stage has Th of 206.5–332 °C (average 280.7 °C) and salinity of 1.6–5.1 wt.% NaCleqv; and the S3 stage has Th of 170.9–328.7 °C (average 246 °C) and salinity of 0.2–5.9 wt.% NaCleqv. Based on the results of the aforementioned investigation, the fluid inclusions in quartz, fluorite, and calcite are mainly H2O-NaCl vapor-liquid two-phase. Additionally, examinations of inclusions in S1 wolframite and coexisting quartz using infrared and microthermometry show that the mineralizing fluid likewise belongs to the NaCl-H2O system. The Th of inclusions in wolframite is ~40 °C higher than that of coexisting quartz. Moreover, the fluid experienced a decrease in temperature accompanied by nearly constant salinity, which indicates that wolframite precipitation is due to fluid mixing and simple cooling, and the precipitation is earlier than quartz. In situ S and H-O isotope data show that the samples have δ34S = −2.58‰ to 1.84‰, and the ore fluids have δD = −76.6 to −51.5‰ (S1 and S2), and δ18Ofluid = −6.6 to −0.9‰ (S1) and −12.9 to −10.2‰ (S2). All these indicate that the mineralizing fluid was derived from the granitic magma at Qianlishan, with substantial meteoric water incursion during the ore stage. Such fluid mixing and subsequent cooling are most likely the primary controls for ore deposition.
Abstract The 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.
Abstract Granitic pegmatite Li deposits account for approximately half of global Li production, while the Li mineralization mechanism remains enigmatic. Here we present Li isotope data on the albite from 8 textural zones of the well-characterized Koktokay No. 3 Li-Be-Nb-Ta-Rb-Cs mineralized pegmatite in Xinjiang, China. Our results reveal that there coexists two important processes during the internal evolution of the pegmatite: (1) fluid exsolution and (2) Li unloading. The former facilitates Li enrichment and the later results in spodumene crystallization. These “fluid transportation” processes can be indicated by a negative correlation between δ 7 Li value and Li content. Globally, the statistical geochemical data of Li mineralized pegmatites have also yielded a negative linear correlation between δ 7 Li value and Li content in both of whole rock and separated mineral samples, providing compelling evidence that “fluid transportation” is the key mechanism responsible for Li mineralization in granitic pegmatites. This finding is of great significance for Li metal deposit modeling, highlighting an urgent need to better understand the dynamic processes of magmatic-hydrothermal interaction during the crystallization of pegmatite magma.
The W-Sn-Pb-Zn polymetallic deposits in the Bozhushan area of Southeastern Yunnan are closely and genetically related to the large Bozhushan granite complex. Whole-rock geochemistry, zircon U-Pb dating and Hf isotope analysis have been carried out to investigate the emplacement age, petrogenesis and formation background of the granite complex. Two stages of granites have been identified in the granite complex. The LA-ICP-MS zircon U-Pb ages of the late granite range from (87.08±0.55) Ma to (87.29 ± 0.69) Ma. All granites are characterized with high contents of SiO2 (63.37%~72.07%) and K2O (4.96%~6.19%), low contents of Fe and Mg, A/CNK values ranging from 1.03 to 2.42, obviously differentiated light and heavy rare earth elements (LREE/HREE=14.0~26.5), obviously negative Eu anomalies ( δEu=0.38~0.62), enriched large ion lithophile elements including Rb, Th and U and rare earth elements including La, Ce, and Nd, and depleted Ba, Ta, Nb, Sr, Y and Yb. Their zircons have εHf(t) values ranging from −9.31 to −5.14. They have geochemical and isotopic characteristics of the high potassium-calcium alkaline peraluminous S-type granite. Their second-stage granite model ages (tDM2) are ranged from 1476 Ma to 1737 Ma, indicating that their magmas could be derived from the partial melting of Early and Middle Proterozoic lower crust materials. The comprehensive research suggests that the Bozhushan granite complex was formed by magmas derived from the partial melting of the Early and Middle Proterozoic lower crustal materials due to the upwelling of the asthenospheric mantle under the extensional setting in the Cretaceous.
The Fule deposit is a typical Cd-, Ge- and Ga-enriched Pb-Zn deposit located in the southeast of the Sichuan–Yunnan–Guizhou Pb-Zn polymetallic ore province in China. Zoned, euhedral cubic and pentagonal dodecahedral and anhedral pyrites were observed, and they are thought to comprise two generations. First generation pyrite (Py1) is homogeneous and entirely confined to a crystal core, whereas second generation pyrite (Py2) forms bright and irregular rims around the former. Second generation pyrite also occurs as a cubic and pentagonal dodecahedral crystal in/near the ore body or as an anhedral crystal generally closed to the surrounding rock. The content of S, Fe, Co, and Ni in Py1 are from 52.49 to 53.40%, 41.91 to 44.85%, 0.19 to 0.50% and 0.76 to 1.55%, respectively. The values of Co/Ni, Cu/Ni and Zn/Ni are from 0.22 to 0.42, 0.02 to 0.08 and 0.43 to 1.49, respectively, showing that the Py1 was formed in the sedimentary diagenetic stage. However, the contents of S, Fe, Co, and Ni in Py2 are in the range from 51.67 to 54.60%, 45.01 to 46.52%, 0.03 to 0.07% and 0.01 to 0.16%, respectively. The Co/Ni, Cu/Ni and Zn/Ni values of Py2 are from 0.40 to 12.33, 0.14 to 13.70 and 0.04 to 74.75, respectively, which is characterized by hydrothermal pyrite (mineralization stage). The different δ34S values of the Py1 (−34.9 to −32.3‰) and the Py2 (9.7 to 20.5‰) indicate that there are at least two different sources of sulfur in the Fule deposit. The sulfur in Py1 was derived from the bacterial sulfate reduction (BSR), whereas the sulfur in the ore-forming fluids (Py2) was derived from the thermochemical sulfate reduction (TSR). The main reasons for the different morphologies of pyrite in the regular spatial distribution in the Fule deposit are temperature and sulfur fugacity.
The Niujiaotang MVT Pb-Zn ore field is located at the southwestern end of the West Hunan-East Guizhou (WHEG) metallogenic belt, which overlaps spatially with the Majiang paleo-oil reservoir. The Pb-Zn mineralization is closely associated with oil-gas accumulation processes. However, the genetic link between the paleo-oil reservoir and the Pb-Zn deposits remains unclear. In this paper, we present new findings of bitumen (paleo-oil reservoir) and its features in the deposits, and apply various isotopic geochemical methods and 2D seismic data to elucidate the source rock and coupling relationship of the paleo-oil reservoir and the Pb-Zn deposits. This study reveals that the ore has a simple mineral composition, mainly comprising sphalerite, pyrite, and dolomite. Solid bitumen occurs widely in the ore and the host dolostone, and coexists with minerals from the mineralization stage. Laser Raman spectroscopy shows that the bitumen in the wall rocks of the Chengong deposit and the Danzhai paleo-oil reservoir are both overmature, and their carbon isotope compositions (δ13CPDB = –29.17 ‰ – –31.20 ‰, average –30.10 ‰, n = 6) and initial 187Os/188Os ratio (1.08±0.19) suggest that they have the Lower Cambrian source rock similar to the Majiang paleo-oil reservoir. The δ34S value of pyrite in the bitumen from the wall rocks in the Chengong deposit ranges from +28.15 ‰ to +44.12 ‰ (average +33.28 ‰, n = 18), which is consistent with the sulfur isotope composition of the ore sulfide reported previously, indicating that they both derived from sulfate in the Middle-Upper Cambrian strata. Bitumen Re-Os and sphalerite Rb-Sr isotopic dating indicate that oil reservoir accumulation in the ore-hosting strata preceded Pb-Zn mineralization, occurring at 424±160 Ma (MSWD = 1.3) and 398±4.7 Ma (MSWD = 0.66), respectively. The initial 87Sr/86Sr ratio of sphalerite is 0.709983±0.000027, which, after comparison and in combination with previous studies, suggests that the metallogenic metals mainly originated from the underlying strata and basement. 2D seismic data show that the Zaolou fault (F2) that controls the mineralization is a deep fault that extends to the basin basement, and acts as a migration pathway for hydrocarbon fluids and ore-forming materials. We propose that liquid hydrocarbons played a significant role in Pb-Zn mineralization, acting as reductants to reduce sulfate through the thermochemical sulfate reduction (TSR) reaction and provide abundant reduced sulfur (H2S/HS−) for Pb-Zn mineralization. Finally, we present a comprehensive model of hydrocarbon accumulation and mineralization in the Niujiaotang ore field.
The Dulong Sn polymetallic deposit is located in the SE Yunnan-West Guangxi ore province, and represents one of the three largest cassiterite-sulfide deposits in China. The deposit is a potential gallium (Ga) deposit in China with abundant tin and zinc resources. However, the occurrence of Ga in the deposit and the control on its mineralogy are still poorly understood. Here, we provide a detailed account of the gallium distribution in silicate, oxide, and sulfide minerals at Dulong, based on field geological and petrographic observations and geochemical analysis. Gallium is mainly hosted in Al-rich minerals, such as muscovite (avg. 139 ppm), biotite (avg. 86.8 ppm), and feldspar (avg. 21.3 ppm), in the ore-related granite. This distribution behavior of gallium is consistent with its predicted partitioning between the phenocrysts and melt. In the Sn ore, chlorite has high Ga content (avg. 104 ppm), probably caused by the gallium tends to form hydroxyl complexes. In contrast, pyroxene and sphalerite have low Ga content (avg. 1.24 and 1.50 ppm, respectively). Meanwhile, two types of magnetite (Mag-I and Mag-II) have been identified based on mineral paragenesis: Mag-I is mainly associated with sphalerite. It is porous, with the pores filled with Ga-rich aluminosilicates (e.g., chlorite), and has high Ga content (avg. of 18.3 ppm). Mag-II is mainly associated with sphalerite, pyrrhotite, and chalcopyrite, and has low Ga (avg. 1.34 ppm). The dissolution of Ga-rich aluminosilicates in magnetite likely provided gallium to magnetite, resulting in higher Ga content in Mag-I. The magnetite Ga content decrease with increasing distance from the mineralization center, and the magnetite mineralization temperature also shows a similar trend. This study confirms that the dominant substitution for Ga in muscovite is Ga3+ ↔ Al3+, and in magnetite it is Ga3+ ↔ Mn2+ + Me+ and Ga3+ ↔ Cu+ + Zn2+. Most of the Ga is hosted in chlorite and magnetite in the highly chloritized sulfide ore at Dulong, which is a critical factor that can significantly affect the estimation of economically recoverable by-product elements in the sulfide ore.
The Nanpanjiang basin hosts the world’s second-largest concentration of Carlin-type gold deposits. To decipher the origin and evolution of hydrothermal fluid, this study conducted Sm–Nd dating, in-situ trace element, and C-O-Sr isotopic analyses on three types of calcite samples from the giant Lannigou gold deposit in the Nanpanjiang basin, SW China. The type-I calcite, intergrown with Au-bearing arsenian pyrite, has an Sm–Nd isochron age of 213 ± 7 Ma (MSWD = 0.81), indicating that gold mineralization occurred in Late Triassic. The type-II calcite, which coexists with high-maturity bitumens and cut through the main-stage gold orebodies, yields an Sm–Nd age of 188 ± 14 Ma (MSWD = 0.34), representing a post-ore hydrocarbon accumulation event. The type-I and type-II calcite samples have low REE contents (5.28–51.6 ppm) and exhibit MREE-enriched and LREE-/HREE-depleted patterns. Combined with their identical C-O-Sr isotopes, we suggest that hydrothermal fluids responsible for the precipitation of type-I and type-II calcite samples were derived from a mixed metamorphic fluid and meteoric water source. In contrast, the type-III calcite samples, associated with realgar and orpiment, have distinct Mn, Sr, and As contents, REE patterns, and C-O-Sr isotopic composition from the type-I and II calcites, suggestive of different fluid sources. Based on our and previously published data, we propose that the fluid evolution, gold mineralization, and hydrocarbon accumulation in the Nanpanjiang basin are closely related to the Indosinian and Yanshanian orogenies in South China.
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