Geochemical characteristics of pyrite in Duolanasayi gold deposit, Xinjiang

The Duolanasayi gold deposit, 60 km NW of Habahe County, Xinjiang Uygur Autonomous Region, is a mid-large-scale gold deposit controlled by brittle-ductile shearing, and superimposed by albitite veins and late-stage magma hydrothermal solutions. There are four types of pyrite, which are contained in the light metamorphosed rocks (limestone, siltstone), altered-mineralized rocks (chlorite-schist, altered albite-granite, mineralized phyllite), quartz veins and carbonatite veinlets. The pyrite is the most common ore mineral. The Au-barren pyrite is present mainly in a simple form and gold-bearing pyrite is present mainly in a composite form. From the top downwards, the pyrite varies in crystal form from {100} and {210} {100} to {210} {100} {111} to {100} {111}. Geochemical studies indicate that the molecular contents of pyrite range from Fe1.057S2 to Fe0.941S2. Gold positively correlates with Mn, Sr, Zn, Te, Pb, Ba and Ag. There are four groups of trace elements: Fe-Cu-Sr-Ag, Au-Te-Co, As-Pb-Zn and Mn-V-Ti-Ba-Ni-Cr in pyrite. The REE characteristics show that the total amount of REE (ΣREE) ranges from 32.35×10 -6 to 132.18×10 -6; LREE/HREE, 4.466-9.142; (La/Yb)N, 3.719-11.133; (Eu/Sm)N, 0.553-1.656; (Sm/Nd)N, 0.602-0.717; La/Yb, 6.26-18.75; δEu, 0.628-2.309; δCe, 0.308-0.816. Sulfur isotopic compositions (δ 34S=-2.46‰--7.02‰) suggest that the sulfur associated with gold mineralization was derived from the upper mantle or lower crust.     

Prediction of hidden Au and Cu–Ni ores from depleted mines in Northwestern China: four case studies of integrated geological and geophysical investigations

Integrated geological and geophysical investigations were carried out in 26 active mines in Northwestern China during the period 2001–2006 to explore for hidden extensions of known ore bodies and to search for new mineralization. This paper presents four case studies from northwest China: the Kuoerzhenkuoa volcanogenic hydrothermal gold deposit, the Nanjinshan breccia-associated gold deposit, the Duolanasayi deposit, associated with a ductile–shear zone, and the Hulu magmatic Cu–Ni sulfide deposit. In these studies, detailed mine-scale geological studies were carried out to determine the location and controls on ore formation. Based on these investigations and a review of previous exploration data, genetic models for the deposits were evaluated, and specific new targets were generated. These target areas were tested with surface geophysical surveys using the Stratagem EH4 system, a hybrid-source magnetotellurics (MT) method. Analysis of the data obtained in the surveys identified geophysical target anomalies that were subsequently drilled. Many of these test holes demonstrate the presence of Au and Cu–Ni mineralization. Evaluation of the geological models was crucial in developing conceptual targets as a basis for surface geophysical surveys. These models established the most likely target areas where Au and Cu–Ni mineralization could occur, but they did not define the limits or the geometries of the mineralized zones. Hybrid MT surveys played an important role in defining the location of buried mineralized systems and in testing the validity of the conceptual targets. The resistivity cross-sections obtained by imaging the MT data established the boundaries and geometries of the host rocks, including the distribution of lithology, structures, alteration, and mineralization. The four case studies in this paper show how this integrated geological and geophysical approach was used successfully to discover hidden mineral deposits.

Geochemical characteristics and source of ore-forming fluid of Duolanasayi gold deposit,Xinjiang

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新疆多拉纳萨依金矿区构造特征与成矿关系

多拉纳萨依金矿发现于20世纪80年代末,近年研究确认该矿与韧性剪切带关系密切,但对于韧性剪切带如何控制金矿床的形成并未进行深入研究。笔者从地质背景、矿床地质,以及控矿构造分析了多拉纳萨依金矿矿床特征及其成矿机理;明确了矿床产于泥盆系托克萨雷组第三岩性段的灰岩-浅变质-硅质岩系,受控于多拉纳萨依韧性剪切带;控矿构造具有二次韧性剪切变形、矿化和多期次脉体矿化的特征,显示出构造活动的多期次性与复杂性,阐明了构造期次与矿化之间的关系。