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Wang P.K.,Oil and Gas Survey | Wang P.K.,Chinese Academy of Geological Sciences | Zhu Y.H.,Oil and Gas Survey | Zhu Y.H.,Chinese Academy of Geological Sciences | And 12 more authors.
Science China Earth Sciences | Year: 2014

A type of authigenic pyrites that fully fill or semi-fill the rock fractures of drillholes with gas hydrate anomalies are found in the Qilian Mountain permafrost; this type of pyrite is known as "fracture-filling" pyrite. The occurrence of "fracture-filling" pyrite has a certain similarity with that of the hydrate found in this region, and the pyrite is generally concentrated in the lower part of the hydrate layer or the hydrate anomaly layer. The morphology, trace elements, rare earth elements, and sulfur isotope analyses of samples from drillhole DK-6 indicate that the "fracture-filling" pyrites are dominated by cubic ones mainly aligned in a step-like fashion along the surfaces of rock fractures and are associated with a circular structure, lower Co/Ni and Sr/Ba, lower ΣREE, higher LREE, significant Eu negative anomalies, and Δ34SCDT positive bias. In terms of the pyrites' unique crystal morphology and geochemical characteristics and their relationship with the hydrate layers or abnormal layers, they are closely related with the accumulation system of the gas hydrate in the Qilian Mountain permafrost. As climate change is an important factor in affecting the stability of the gas hydrate, formation of fracture-filling pyrites is most likely closely related to the secondary change of the metastable gas hydrate under the regional climate warming. The distribution intensity of these pyrites indicates that when the gas hydrate stability zone (GHSZ) is narrowing, the hydrate decomposition at the bottom of the GHSZ is stronger than that at the top of the GHSZ, whereas the hydrate decomposition within the GHSZ is relatively weak. Thus, the zone between the shallowest and the deepest distribution of the fracture-filling pyrite recorded the largest possible original GHSZ. © 2014 Science China Press and Springer-Verlag Berlin Heidelberg.

Jiang S.-Q.,Chinalco Resources Corporation | Jiang S.-Q.,China University of Geosciences | Sun X.-G.,Chinalco Tibet Mining Company | Yang T.-Z.,Chinalco Resources Corporation | And 4 more authors.
Geology in China | Year: 2014

Located in the northern margin of the Tibetan Plateau, the Duolong Cu-Au ore concentration area has typical geological setting and metallogenic dynamic background, which is quite unique in porphyry copper deposits of Tibet. The effective geological exploration model for Duolong is of great significance. This paper focused on metallogenic system and exploration model in this area. Several important results were obtained through detailed field and laboratory studies: © Copper and gold ore bodies are preserved in altered (feldspathic) quartz sandstone and volcanic rocks of Jurassic Quse Formation and Sewa Formation. Three alteration zones exist from the center of ore-bearing porphyry outwards, i.e., potassium-silicified and sericitized zone, sericitized zone, and pyritized-hornfelsic zone. © The spacial layout of mineralization in this area finds expression in "three ore belts and five ore fields". The three belts are distributed in en echelon shape, i.e., Naruo-Sena-Gaerqin Cu-Au belt, Duobuza-Bolong-Tiegelongnan Cu-Au-Mo belt, and Dibaonamugang Cu-Au belt, whereas the five blocks are ore zones located in the three belts, i. e., Naruo-Saijiao-Rongna, Gaerqin, Dibaonamugang, Duolong-Duobuza and Tiegelongnan ore fields. © The model of "four effective approaches to exploration" has been summarized: (1) Iron caps, malachites and porphyry intrusions are direct indicators for porphyry coppe depositsr; (2) Low magnetic anomalies reflect the granodiorite porphyry ore rock indirectly; (3) High-polarization areas directly reflect sulfide zones surrounding both sides of the ore body, and indirectly reflect the copper ore body wrapped in the pyrite zone; (4) Copper and gold geochemical anomalies indicate regional enrichment of ore-forming elements. The application of this model to Naruo and Rongna areas led to the effective discovery of the deep-buried porphyry copper deposit. The exploration breakthrough in the Duolong area has been achieved on the basis of this exploration model.

Jiang S.-Q.,Chinalco Resources Corporation | Jiang S.-Q.,Chinese Academy of Geological Sciences | Jiang S.-Q.,China University of Geosciences | Hao Z.-G.,Chinese Academy of Geological Sciences | And 3 more authors.
Geological Bulletin of China | Year: 2011

In order to study the Damoqujia gold deposit located in the Zhaoyuan - Pingdu fault zone in eastern Shandong Province, the authors selected an area with typical structural characteristics to conduct magnetic fabric investigation. 112 core samples with direction signals were collected at 36 sampling points in different structural parts of the fault zone, and all samples were arranged along the exploration lines. Magnetic fabric studies show that the study area is dominated generally by weakly magnetic rocks. Magnetic susceptibility has a higher value in metamorphic rocks of the Jiaodong Group; nevertheless, the magnetic susceptibility seems to be lower in biotite granite, especially in strongly altered rocks subjected to high extent of fragmentation. Magnetic anisotropy shows that the rocks extruded in NE direction, and the regional compressive stress direction of the tectonic stress field indicated by the magnetic fabrics is similar to that of the Damoqujia ore deposit. A comparison between the magnetic fabric anisotropy (P value) along No. 80-81 lines and the Au content of rocks subjected to different degrees of mineralization reveals that the P value is negatively correlated to gold grades. Gold mineralization of weakly mineralized mylonite is comparatively hosted in magnetic-foliation-developed rocks. At the late stage of mineralization, gold content changed negatively with the values of rock magnetism; especially the relative tension quartz vein, which had the highest gold content due to the filling of ore fluids during the relaxation phase of the strong strain area.

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