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Peng H.-J.,Chengdu University of Technology | Zhang C.-Q.,Chinese Academy of Geological Sciences | Mao J.-W.,Chinese Academy of Geological Sciences | Santosh M.,China University of Geosciences | And 2 more authors.
Journal of Asian Earth Sciences | Year: 2015

The Late Cretaceous Hongniu-Hongshan porphyry-skarn copper deposit is located in the Zhongdian area of northwestern Yunnan Province, China. Garnets from the deposit have compositions that range from Adr14Grs86 to almost pure andradite (Adr98Grs2) and display two different styles of zoning. The garnets are predominantly of magmatic-hydrothermal origin, as is evidenced by their 18Ofluid (5.4-6.9‰) and low Dfluid (-142‰ to -100‰) values, both of which likely result from late-stage magmatic open-system degassing. Three generations of garnet have been identified in this deposit: (1) Al-rich garnets (Grt I; Adr22-57Grs78-43) are anisotropic, have sector dodecahedral twinning, are slightly enriched in light rare earth elements (LREEs) compared with the heavy rare earth elements (HREEs), have negative or negligible Eu anomalies, and contain high concentrations of F. Fluid inclusions within these Al-rich garnets generally have salinities of 12-39wt.% NaCl eq. and have liquid-vapor homogenization temperatures (Th) of 272-331°C. The Grt I are most likely associated with low- to medium-salinity fluids that were generated by the contraction of an ascending vapor phase and that formed during diffusive metasomatism caused by pore fluids equilibrating with the host rocks at low W/R (water/rock) ratios. These garnets formed as a result of the high F activity of the system, which increased the solubility of Al within the magmato-hydrothermal fluids in the system. (2) Fe-rich garnets (Adr75-98Grs25-2) have trapezohedral faces, and are both anisotropic with oscillatory zoning and isotropic. These second-generation Fe-rich garnets (Grt II) have high σREE concentrations, are LREE-enriched and HREE-depleted, and generally have positive but variable Eu anomalies. All of the Fe-rich garnets contain high-salinity fluid inclusions with multiple daughter minerals with salinities of 33-80wt.% NaCl eq. Some of them show higher temperatures of halite dissolution (465-591°C) than liquid-vapor homogenization temperatures (319-473°C), and several Fe-rich garnets contain inclusion groups indicative of boiling. The Grt II are associated with high-temperature, hypersaline fluids that were segregated from magma at a depth of at least 5.6km and reacted with carbonates at depths shallower than 2.0km. (3) Al-rich garnet veins (Adr14-60Grs86-40) contain allotriomorphic crystals, have lower HFSE (high field strength element) and REE concentrations than the other garnets, and have HREE-enriched and LREE-depleted patterns with small Eu anomalies that are typical of the majority of garnets. The Grt III most likely formed from residual metasomatic fluids. © 2014 Elsevier Ltd.


Peng H.,Chinese Academy of Geological Sciences | Li H.Y.,Chinese Academy of Geological Sciences | Pei R.F.,Chinese Academy of Geological Sciences | Zhang C.Q.,Chinese Academy of Geological Sciences | And 4 more authors.
Acta Petrologica Sinica | Year: 2014

The Hongniu-Hongshan deposit is a newly discovered porphyry-skarn copper deposit in Zhongdian volcanic arc, which belongs to Southwest Sanjiang metallogenic belt. The deposit occurs within the hydrothermal alteration zone of the Yanshanian felsic intrusion which emplaced into Triassic carbonate and marble. The biotite and amphibole phenocryst in the quartz monzonite porphyry related to the mineralization contain abundant fluorine, respectively reached 1.49% and 2.62%, indicating that the magma are rich in water and fluorine. The quartz phenocryst show a skeletal texture, which indicate the magma undergone rapid rising, and the growth embayments, resorption surfaces, and high-K edge indicate the quartz phenocryst undergone autometasomatic process. In addition, the magmatic hydrothermal breccias in a drill core suggest that magmatic hydrothermal breccias were generated by explosive, fluid released from crystallizing porphyry, and there probably be concealed porphyry in the deep. The prograde stage coule be divided into three main substage: aluminum-riched garnets (And22-57) and diopside (Hd7-27) in the first substage formed by diffusive metasomatism, and the fluid formed from high temperature magmatic degassing: Iron-riched garnets (And75-98) and pyroxenes (Hd10 99) in the second substage formed by advective metasomatism, and the large scale fluid formed by magmatic fluid exsolution: The skarn mineral veins in the last substage probably formed from residual fluid of the metasomatism. The formation of skarn lead to the CO 2 lost, mineral volume decreased, and open space created, permeability and porosity increased, which well-produced for mineralization. In the retrograde stage, the mineral assemblage mainly is epidote, amphibole, chlorite and sulfides. In the early retrograde stage, porosity decreased owning to hydrous minerals, fluid pressure increased leaded to fluid boiling and cryptoexplosion, as the result, the fluid temperature and pressure decrease, and copper precipitation. In the last stage, owning to the repeated boiling of fluid, formed open system, acidic magmatic fluid mixed with atmospheric water, copper precipitation.


Peng H.-J.,Chinese Academy of Geological Sciences | Mao J.-W.,Chinese Academy of Geological Sciences | Pei R.-F.,Chinese Academy of Geological Sciences | Zhang C.-Q.,Chinese Academy of Geological Sciences | And 4 more authors.
Journal of Asian Earth Sciences | Year: 2014

The Hongniu-Hongshan porphyry and skarn copper deposit is located in the Triassic Zhongdian island arc, northwestern Yunnan province, China. Single-zircon laser ablation inductively coupled plasma mass spectrometry U-Pb dating suggests that the diorite porphyry and the quartz monzonite porphyry in the deposit area formed at 200Ma and 77Ma, respectively. A Re-Os isotopic date of molybdenite from the ore is 78.9Ma, which indicates that in addition to the known Triassic Cu-(Au) porphyry systems, a Late Cretaceous porphyry Cu-Mo mineralization event also exists in the Zhongdian arc. The quartz monzonite porphyry shows characteristics of a magnetite series intrusion, with a high concentration of Al, K, Rb, Ba, and Pb, low amount of Ta, Ti, Y, and Yb, and a high ratio of Sr/Y (average 26.42). The Cretaceous porphyry also shows a strong fractionation between light and heavy rare earth elements (average (La/Yb)N 37.9), which is similar to those of the Triassic subduction-related diorite porphyry in the Hongniu-Hongshan deposit and the porphyry hosting the Pulang copper deposit. However, in contrast to the older intrusions, the quartz monzonite porphyry contains higher concentrations of large ion lithophile elements and Co, and lesser Sr and Zr. Therefore, whereas the Triassic porphyry Cu-(Au) mineralization is related to slab subduction slab in an arc setting, the quartz monzonite porphyry in the Hongniu-Hongshan deposit formed by the remelting of the residual oceanic slab combined with contributions from subduction-modified arc lithosphere and continental crust, which provided the metals for the Late Cretaceous mineralization. © 2013.


Zhang J.,China University of Geosciences | Su Q.,China University of Geosciences | Liu X.,China University of Geosciences | He Z.,Yunnan Gold Mining Industry Group | And 3 more authors.
Yanshi Xuebao/Acta Petrologica Sinica | Year: 2014

The Dian-Qian-Gui area, located in the southwestern Yangtze craton, is one of the most important Carlin-type (disseminated) gold concentration areas in China. The regional Mile-Shizong fault, Nanpanjiang fault and Fu'ning fault etc. controlled the tectonic deformation and the deposit location. In the Dian-Qian-Gui gold triangle area, the Laozhaiwan gold deposit, owning 31. 40t proven gold reserves at present, is the only large Carlin-type gold deposit discovered in Yunnan Province and possesses the features of simple ore minerals, disseminated gold, low gold grade and large tonnage. This gold deposit includes three ore sections, i. e., the Yuanjiaping, Chunshuwan and Laoyingshan sections. The occurrence of ore bodies are mainly controlled by the unconformity surface and fold or fault structures in the ore district. The ore bodies are dominantly hosted in the Lower Devonian Posongchong Formation which is above the Caledonian unconformity and mainly consists of gray, brown and yellow thick fine sandstone. The largest orebody V3 occurs in the Chunshuwan section; and the gold grade obviously increases where the later diabase dyke invaded along the NW-trending F7 fault. The hydrothermal ore-forming process can be divided into early, middle and late three stages, which are characterized by the quartz-pyrite, quartz-pyrite-sericite and stibnite-calcite assemblages respectively. In this paper, we analyzed the H-0 isotopic composition of the quartz and ore-forming fluid and S-Pb isotopic composition of the sulfides from different ores at Laozhaiwan. The δDH2Ovalues ranges between - 109‰ and -93‰, while the δ18OH2Ovalues of the early, middle and late stage are 7. 8‰ ∼9. 2‰, 5. 9‰ ∼7. 0‰ and 2. 70‰ respectively and plotted in the different origin area. The H-O isotopic study indicates that the ore-forming fluid in early stage was initially sourced from metamorphic devolatilization or partial formation water from the sedimentary strata, in middle stage the magmatic water played an important role for the some gold enrichment, and in late stage gradually mixed with meteoric water. The δ S values of different ores and altered rocks range from 2. 096‰ to 32. 289‰, with peaks ranging from 2‰ to 8‰. The δ34S values of two pyrite samples from early-stage altered rocks are 6. 115‰ and 6. 412‰, the δ34S values of five stibnite samples from late-stage Sb-ores are 2. 096‰ ∼4. 691‰, at the same time the pyrite samples from middle stage ore show a wide δ34S value range, which suggesting that the multi-sources of sulfur in metallogenesis. The lead isotopic compositions of ore sample are 206Pb/204Pb = 18. 178 ∼ 18. 992, 207Pb/204Pb = 15. 635 ∼ 15. 774 and 208Pb/204Pb = 38. 456 ∼ 39. 051, indicating the ores are rich in U-radiogenic Pb. The studies on S-Pb isotope systematics show that the ore-forming elements were mainly derived from the ore-hosted sedimentary strata as well as magmatic activity. The available ESR dating of the quartz from diabase is 64.8 ± 6.5 Ma indicating that the ore-forming process mainly took place in the Late Yanshanian to Early Himalayan period. The formation of the Laozhaiwan gold deposit experienced the initial enrichment in Early Devonian period, the extraction, migration and enrichment by metamorphic/magmatic hydrothermal system in Late Yanshanian to Himalayan period; and finally the secondary oxidation and enrichment after hydrothermal mineralization.


Peng H.-J.,Chinese Academy of Geological Sciences | Zhang C.-Q.,Chinese Academy of Geological Sciences | Zhou Y.-M.,Yunnan Gold Mining Industry Group | Tian G.,China University of Geosciences | And 4 more authors.
Geology in China | Year: 2012

The Hongniu deposit is located in the Zhongdian island arc belt of northwest Yunnan and lies in the middle part of southwest Sanjiang region, belonging to the southern segment of the Triassic Yidun island arc belt. This ore deposit is one of the promising copper-polymetallic deposits with vast potential, and its Cu reserves have reached the middle size. Geological features of the ore bodies and element geochemical characteristics indicate that Hongniu is a typical skarn - hornfels type copper polymetallic ore deposit. It has typical alteration zoning and metallogenic element zoning of the skarn type deposit in both vertical and horizontal directions. The?element geochemical characteristics of the skarn are obviously affected by the elements of marble and quartz monzonite porphyry. According to geological features of the ore bodies, the authors also infer that the deep porphyry bodies have great metallogenic potential.


Gao X.,China University of Geosciences | Deng J.,China University of Geosciences | Meng J.,China University of Geosciences | Yan H.,China University of Geosciences | And 4 more authors.
Acta Petrologica Sinica | Year: 2014

The Hongniu deposit is a newly discovered skarn type copper deposit in Geza volcanic-magmatic arc which is located in the southern part of Yidun island arc. Its copper reserves have reached the large size. Distinctly different from the typical skarn deposits, its skarn and hornfels usually arranged alternately, consisting with the attitude of stratum. Skarn is not in direct contact with the intrusive rocks but direct contact with the marble. There are coarse garnet and wollastonite visible in the marble. While, there also have marble xenoliths in the skarn. Therefore, the Hongniu copper deposit is the product of concealed intrusive rocks, belonging to the distal skarn type. According to the combination of skarn minerals, the skarn type can be divided into garnet skarn, garnet-diopside (or diopside-garnet) skarn, diopside skarn, idocrase-garnet skarn, wollastonite-garnet skarn, epidote-garnet skarn, actinolite-epidote skarn, wollastonite skarn and epidote skarn. Among these types, the garnet skarn, diopside skarn and wollastonite skarn are the most common. Garnet is the most important skarn mineral in the Hongniu deposit, and it is therefore significant to study characteristics of garnet due to its wide distribution, various colors and strong mineralization. Through systematic field work and the made-up of drill holes (0ZK10, 3ZK11 and 7ZK16), the paper summarizes the garnet distribution in space and mineralized characteristics in Hongniu deposit, collecting some fresh garnet skarn and a small amount of skarnized marble to make thin sections, and carrying out detailed microscopic identification, to induce the characteristics of garnet including color, shape, structure, petrography, and analyzed its chemical composition by electron probe. Garnet has two obvious stages. Early garnets are widely distributed, brown-red to brown, hypidiomorphic-idiomorphic medium grained texture, with anomalous optical characteristics on the cross-polarized light, and their particle size is generally between 0.2 ∼4mm, developing zonation patterns. Changes in the content scope of the SiO2is 35.18% ∼ 37.69%, CaO is 33.34% -36.35%, A12O3is 3.64% ∼ 13.69%, FeO is 11.90% -24.18%, MgO is 0.00%-0.08%, and there is a negative correlation between the content of FeO and Al2O3, while an overall positive correlation between the content of SiO2and CaO. The end members of garnet are mainly andradite (36.88% -82.36%), followed by grossular (16.59% -60.75%), and there are a small number of pyrope, almandine and spessartine, belonging to andradite-grossular series (And37 82Gro17-61Spe + Pyr + Alm0.33-3.71). The garnets of later stage are brownish to light red, usually veinlike distributed in skarnized hornfels and marble, also can be seen in some kinds of skarn, with hypidiomorphic-xenomorphic granular structure. Changes in the content scope of the SiO2is 35.06% -36.27%, CaO is 33.07%-33.77%, A12O3is 0.04%-1.05%, FeO is 27.38% -28.18%, MgO is 0.00% -0.04%, the composition of end members belongs to andradite. Changes in contents of major elements in zoned garnet shows a certain regularity, from the core to the rim, the content of FeO increased, the content of Al2O3decreased, the content of andradite increased, the content of grossular decreased, reflecting the diagenetic environment was acidic and reduced with low oxygen fugacity when the garnet began to form. During the process of the crystal formation, the oxygen fugacity increased, and the ore-forming solution shifted from acidic to weakly alkaline, causing the precipitation of metal sulfide. Chalcopyrite, pyrrhotite, molybdenite usually fill between garnet grains, or form veinlets in the cracks of crystal, or replace along the garnet growth zoning surface, showing that the garnets form prior to the mineralization of copper and can provide space for the precipitation and enrichment of metals.


Peng H.-J.,Chengdu University of Technology | Peng H.-J.,Chinese Academy of Geological Sciences | Peng H.-J.,James Cook University | Mao J.-W.,Chinese Academy of Geological Sciences | And 7 more authors.
Economic Geology | Year: 2016

The Hongniu-Hongshan Cu skarn deposit (77.8 Mt at 1.8% Cu) is located in the central part of the Zhongdian porphyry and skarn Cu belt in southwestern China. Skarn and orebodies occur mainly between the different units of the Upper Triassic Qugasi Formation or within altered limestone adjacent to Late Cretaceous intrusions (78-76 Ma). Three main paragenetic stages of skarn formation and ore deposition have been recognized on the basis of petrographic observations: (1) pre-ore-stage hornfels with diopside (Di87-72Hd12-7), small-scale endoskarn with reddish grossular (Adr22-57Gr78-43), diopside (Di83-92Hd7-15), vesuvianite, and abundant exoskarn with red-brown andradite (Adr75-98Gr2-22), sahlite (Di28-41Hd58-71), and wollastonite; (2) syn-ore-stage retrograde minerals, sulfides (pyrite, chalcopyrite, pyrrhotite, molybdenite, galena, and sphalerite), quartz, and calcite; and (3) post-ore-stage calcite veins. Sulfur isotope values of sulfides are relatively high, with an average δ34S = 4.9% (n = 40), suggesting that the ore-forming fluid was magmatic and that the sulfides precipitated from a relatively reducing ore fluid. The coexistence of silicate melt and primary fluid inclusions in quartz phenocrysts of the mineralizationrelated quartz monzonite porphyry indicates the simultaneous entrapment of fluid and melt, and records the process of the aqueous fluid exsolving from the crystallizing melt. The initial single-phase fluid has a salinity of 8.8 to 12.7 wt % NaCl equiv and homogenization temperatures of 566° to 650°C, corresponding to pressures of 680 to 940 bar and lithostatic depth of 2.5 to 3.5 km. The primary fluid inclusions in the pre-ore-stage garnet and pyroxene composed of coeval vapor-rich (V type) and halite-bearing (S-I and S-II types containing sylvite) inclusions (32->79 total wt % salts) share similar homogenization temperatures (450°-550°C), indicative of the occurrence of fluid unmixing under lithostatic pressures of ∼550 to 780 bar (>2.0-km depth). Primary fluid inclusions trapped in syn-ore quartz, calcite, and epidote show the common development of S-type inclusions (∼37.3 wt % NaCl equiv) with coexisting V-type, liquid-rich (L type), and CO2-bearing (C-I type) inclusions, all of which have homogenization temperatures of 300° to 400°C and trapping pressures of 100 to 400 bar (∼1.5-km depth). Brine inclusions homogenized by halite dissolution after vapor disappearance in both the pre- and syn-ore stages are interpreted to have been trapped under overpressured conditions (>1,520 bar). Oxygen isotope analyses were conducted on garnet, wollastonite, epidote, quartz, and calcite. The pre-orestage garnet and wollastonite have δ18Ofluid values of 5.6 to 8.1%, whereas the syn-ore-stage epidote, quartz, and calcite have more variable δ18Ofluid values in the range of 3.9 to 17.5%. The δ18Ofluid values of the postore-stage vein calcite (15.2-21.3%) are much higher than both the pre- and syn-ore stages. The vapor phase of inclusions contains H2S, CH4, and C2H6 in the syn-ore stages. All these observations reveal that (1) the formation of the Cu skarn deposit was dominated by a magmatic hydrothermal system, (2) multiple fluid pulses contributed to the formation of the pre- and syn-ore-stage skarn minerals and sulfides, and (3) the increase in pH due to the neutralization of the acidic fluid could be the main factor controlling the large-scale ore deposition in Hongniu-Hongshan. © 2016 Society of Economic Geologists, Inc.

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