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Li J.,Chinese Academy of Geological Sciences | Chen W.,Chinese Academy of Geological Sciences | Yong Y.,Chinese Academy of Geological Sciences | Yang L.,Kunming University of Science and Technology | And 4 more authors.
Acta Petrologica Sinica | Year: 2014

The Yangla copper deposit is located in Deqin Vounty, Yunnan Province, which is between the N-S-striking Jinshajiang and Yangla faults. The deposit has copper reserves of about 1. 2Mt and has great potential for further exploration. Yangla copper deposit consists 4 ore blocks from north to south. The Linong ore block, Lunong ore block and Jiangbian ore block are the main copper deposit areas. The Linong ore block is the largest and is related to Linong granodiorite. Many researches have been done in previous studies; however, the ore genesis of the deposit is still debated. Previous researches are mainly in ore-bearing rock-bodies, lack of systematic study on the main copper deposit areas. In this paper, the samples analyzed for petrology, geochemistry and chronology, is collected from marginal phase of Linong granodiorite. The geochemical characteristics show that the samples are enriched in large ion lithophile elements (LILE) and depleted in high field strength element (HFSE). All samples have the characteristics of negative Eu anomalies, LREE/HREE is 9. 38 ∼ 10. 23, and LREE enrichment. All the characters above indicate that Linong granodiorite is contributed from the continental crust. Major element discriminate that Linong granodiorite is continental collision granitoids (CCG). The zircon U-Pb age of Linong granodiorite is 227. 73 ±0. 99Ma (MSWD =0. 098), which indicates the rock mass emplacement era. Combining with previous studies, we can preliminary identified that, 1) Linong granodiorite is continental collision granitoids, based on zircon U-Pb age, in the Late Triassic (before 227Ma), Jinshajiang suture zone is closed and into the continental collision stage; 2) The Yangla copper deposit is a structure ore-control deposit. Linong granodiorite experienced a relatively slow cooling process from 239Ma to 227Ma, mineral assemblages enriched in the magmatic hydrothermal during the process. After rapid uplift and cooling event happened within the region in 227Ma, temperature and pressure changed. The proper fold and fault provide passage and room for ore fluid transportation and accumulation. Yangla copper deposit entered the main mineralization stage.

Yang Z.,China University of Geosciences | Yang L.,China University of Geosciences | Liu J.,China University of Geosciences | Meng J.,China University of Geosciences | And 4 more authors.
Acta Petrologica Sinica | Year: 2014

Yangla copper deposit is one of the important and large deposit located in the middle part of the Sanjiang Tethys metallogenic belt. However, its ore genesis remains unresolved. In Linong ore block, the most important part of the deposit, the principal metallic minerals include chalcopyrite, pyrrhotite and pyrite. The pyrrhotite ores are the most important sulfide ores type. In this study, we have performed the mineragraphy, electro-probe microanalyzer and X-ray diffraction analysis on the pyrrhotite samples from the Linong to analyze the typomorphic characteristics of morphology, composition and texture of pyrrhotite. The results above reveal the ore forming environment and precipitated mechanism of the pyrrhotite, which provide valid constraints on the ore genesis. The geological characteristics are discussed fully and summarized in detail here. Its ore bodies are typically layered or bedded in the interlay er fissure of stratum, closely related to the granodiorite and skarn and controlled by the combination of the pluton, stratum and structures, which show obvious features of the skarn deposit. The pyrrhotite has iron black, bronze, massive and disseminated structure. Microscopically, it shows yellowish-white, snuff, without internal reflection and heterogeneity, anhedral to subhedral granular structure. Locally, the pyrrhotite is cut by quartz-pyrite-chalcopyrite-calcite vein, and the chalcopyrite developed in sphalerite as droplet or foliaceous shape. The pyrrhotite in the Yangla copper deposit, have content of Fe: 59. 25% ∼ 60. 25%, average: 59. 71% and S element: 39. 10% ∼ 39. 97%, average: 39. 52%, and hence the chemical formula is Fe6S7∼ Fe8S9. The average value of crystal cell parameters is similar, a¯0= 11.912Å, b¯0=6. 859Å, c¯0= 12. 813Å, and the crystal powder X-ray diffraction profiles of pyrrhotite shows a double-peak phenomenon with nearly equal intensity, which are main characteristics of the monoclinic pyrrhotite. Accordingly, in the sulphur-rich, rapid cooling and non-uniform stressed conditions, the hexagonal pyrrhotite turns into monoclinic pyrrhotite. During the process, the sulfur of pyrrhotite was in the form of S2-, the content of the iron in pyrrhotite lattice reduced somewhat and the electronegativity of Fe1-xS increased slightly which thus enhanced reducibility. In the Fe-S phase diagram, pyrrhotite locates in the monoclinic pyrrhotite-pyrite zone, which indicates that the ore-forming temperature is about 250°C and that the ore bodies were formed in the sulphur-rich, reductive and non-uniform stress environment. The pyrrhotite shows high content of Co and low content of Ni, while the Co/Ni ratio has a large range, which is consistent with the skarn copper deposit. All the geological and mineralogy typomorphic characteristics of pyrrhotite above suggest that the Yangla copper deposit is a typical skarn type deposit. The geological setting and geochemical characteristics suggest the ore-forming processes as follows: in the early Late Triassic, the tectonic regime transformation from collision-related compression to extension caused tensional characteristics superposed on the former thrust faults along which the ore-bearing magma intruded and contacted with the wall rocks (mainly Linong Formation marble). With the addition of the meteoric water, the magma and ore-forming hydrothermal rapidly cooled, and the open environment gradually became closed, high-pressure and reductive, which led to reduce of the copper solubility and the formation of the Yangla copper deposit.

Yang X.-A.,China University of Geosciences | Liu J.-J.,China University of Geosciences | Cao Y.,China University of Geosciences | Han S.-Y.,China University of Geosciences | And 3 more authors.
Lithos | Year: 2012

The Yangla copper deposit, situated in the middle section of Jinshajiang tectonic belt between Zhongza-Zhongdian block and Changdu-Simao block, is a representative and giant copper deposit that has been discovered in Jinshajiang-Lancangjiang-Nujiang region in recent years. There are coupled relationships between Yangla granodiorite and copper mineralization in the Yangla copper deposit. Five molybdenite samples yielded a well-constrained 187Re- 187Os isochron age of 233.3±3Ma, the metallogenesis is therefore slightly younger than the crystallization age of the granodiorite. S, Pb isotopic compositions of the Yangla copper deposit indicate that the ore-forming materials were derived from the mixture of upper crust and mantle, also with the magmatic contributions. In the late Early Permian, the Jinshajiang Oceanic plate was subducted to the west, resulting in the formation of a series of gently dipping thrust faults in the Jinshajiang tectonic belt, meanwhile, accompanied magmatic activities. In the early Late Triassic, which was a time of transition from collision-related compression to extension in the Jinshajiang tectonic belt, the thrust faults were tensional; it would have been a favorable environment for forming ore fluids. The ascending magma provided a channel for the ore-forming fluid from the mantle wedge. After the magma arrived at the base of the early-stage Yangla granodiorite, the platy granodiorite at the base of the body would have shielded the late-stage magma from the fluid. The magma would have cooled slowly, and some of the ore-forming fluid in the magma would have entered the gently dipping thrust faults near the Yangla granodiorite, resulting in mineralization. © 2012 Elsevier B.V.

Yang X.,China University of Geoscicnces | Liu J.,China University of Geoscicnces | Han S.,China University of Geoscicnces | Zhang H.,China University of Geoscicnces | And 3 more authors.
Acta Petrologica Sinica | Year: 2011

The Yangla copper deposit, situated in the middle section of Jinshajiang joint belt between Zhongza-Zhongdian plate and Changdu-Simao plate, is a representative and giant copper deposit that has been discovered in Jinshajiang-Lancangjiang-Nujiang region in recent years. There are coupled relationship between Linong granodiorite and copper mineralization in the Yangla copper deposit. LA-ICP-SB zircon U-Pb dating has revealed that the ages of two samples from the Linong granodiorites are 234. 1 ± 1. 2Ma ( MSWD = 0. 66) and 235. 6 + 1. 2Ma (MSWD =0. 66) , respectively. Molybdenite Re-Os model age for the KT2 ore body in Linong ore block is 230. 9 ± 3. 2Ma. The former represents the diagenetic age of the Linong granodiorite, the latter represents the metallogenic age of the Yangla copper deposit, the result shows that the metallogenic age is close to diagenetic age, but a little later. It is the significance for finding out genetic type of the Yangla copper deposit and prospecting.

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