The Potential for Prospecting of Lengshuigou Porphyry Copper Deposit in Zhashui‐Shanyang Basin, Shaanxi Province

basin, between Shangzhou-Danfeng and FengzhenShanyang suture zone. Its tectonic environment is fore-arc basin of middle Qinling based on comprehensive studies of tectonic and sedimentary facies etc (Wang et al., 2009). In the area the main strata is Liuling Group, and it is a set of littoral-neritic facies and delta facies combination (Yang , 1991). The tectonic faults are developed, the major is east-west, the minor is northwest, nearly southnorth and north-east direction. Multi-stage tectonic movements provide a beneficial routeway for migration of oreforming elements. The magmatic activity was strong, and lots of acid-intermediate small intrusive bodies, mainly in Indosinian and Yanshanian period, such as Xiaohekou rock, Chigou rock, Lengshuigou rock (141~150Ma). Lots of those rocks are located at intersection part of faults, some show ring-structure characteristic and divided into Shanyang–Fengzhen and Miaogou–Xiaoxigou granite belts from remote sensing image (Yan et al, 2014). The deposits related to magma activity are on both sides along the two granite belts. Fe, Cu, Au, Ag, Pb, Zn, Mo are the main minerals and controlled by EW-NW faults (Wang et al., 2012). The recent studies show that Cu polymetallic ore deposits in this region can be divided into six types: exhalation sedimentationreformed type, sedimentary–reformed type, porphyry type, skarn type, breccia type, hydrothermal vein type. Porphyry copper deposit has an important significance for Qinling, such as Chigou and Lengshuigou porphyry. In this text, we focus on discussing porphyry copper deposit in Lengshuigou. Lengshuigou porphyry copper deposit is located at the south of Shanyang–fengzhen fault and west of Douling– Xiaomaoling chain uplift. The main strata is Devonian elastic and carbonate rocks. Tectonic and magmatic activity is frequent, and formed Lengshuigou complex body, as a stock or apophysis. It can be divided into two stages: Neoproterozoic granite and albite, age is 718705Ma, with little Cu(Mo) mineralized; Yanshanian granodiorite-porpgyry, zircon U-Pb isotopic age is 143145Ma, with disseminated and fine vein chalcopyrite and molybdenite. The Re-Os isotopic age of molybdenite is 145Ma, shows closed correlations with Yanshanian magmatism, and little with Neoproterozoic granite, so this paper lays emphasis on the former. The geochemical characteristics of granite show rich Si and K, poor Na, high-K calcium-alkali to shoshonite series, most of A/ CNK is less than 1.1, quasi-aluminous; rich Ba, K etc LILE, high Pb, poor Nb, Ta, Ti etc HFSE, no significant anomalies of Eu and Ce, similar to typical porphyry (Rui et al., 2004). They fall into the field of post-collision on the tectonic discrimination plots of R1-R2. From Nd-Sr, Lu-Hf isotope and EPMA analysis of biotite and amphibole, dark amphibole distibut unevenly, most clustered and little sporadical under the microscope. It is probably that amphibole formed early was brought into the later magma. Most of eldspar is medium-ultrabasic, some quartz is brought later. It seems that the tectonic setting is the transformational stage of extrusion to stretch, maybe caused by lithosphere delamination. The condition is benefit for porphyry mineralization (Hou et al., 2009; Richard, 2009). The oxidative-reductive condition has an important influence to porphyry mineralization. The logfO2 of granite porphyry in Lengshuigou is -11~-11.5 through biotite pressure calculation (Wu, 2013). Forming in high oxygen fugacity is conducive to mineralization. Physical MENG Deming, WANG Ruiting, WANG Peng and LIU Kai, 2014. The Potential for Prospecting of Lengshuigou Porphyry Copper Deposit in Zhashui-Shanyang Basin, Shaanxi Province. Acta Geologica Sinica (English Edition), 88(supp. 2): 580-581.