The Granitoid Geological And Geochemical Characteristics Of The Gaerqiong Cu-Au Deposit And Relationship Between Granitoid And Mineralization, Tibet

Gaerqiong Cu-Au deposit is recently discovered significant Cu-Au deposit at the western segment of the Bangonghu-Nujiang metallogenic belt, locates at the western segment of the Bangonghu-Nujiang suture zone which is between Nyainqentanglha slab and South Qiangtang slab. Regional tectonic line was the North West towards. The Bangonghu-Nujiang suture zone began to subduct in the later period of middle-late Jurassic Epoch at Shiquanhe(166.4Ma). Mining area of the unique tectonic position resulted in a strong tectonic magmatism, especially the late Yanshanian mixing granodioritic magma at the Qiyiqiao in the east of mining area(At the west of work area about35km),which brought about favorable properties and heat source conditions for copper-gold polymetallic mineralization.The stratum exposed in the mining area is cretaceous Duoai Formation (K1d),which is mainly carbonate rocks,volcaniclastic rocks, terrigenous clastic rocks. Lithological character is mainly limestone, marble, volcanic breccia, tuff, hornfels and mineralization close to the limestone, marble, hornfels. The fault structures are well developed, mainly are North-east trending faults, followed by the NS-trending faults and secondary cracks. There are three main fault structure.F1and F2are NE-SW trending, fault activities are of multi-stage. Early period are tensile stress normal faults and early period are extruded translational thrust fault. Orebodys are controled by F1, F2and a series of other sub-tectonic fault system relationed with F1, F2. Neutral-acidic intrusions of the Late Yanshanian widely distributed in the mining area, with the batholith, strains of rock, rock sticks, dikes, etc. Intrusive contact relationship was between intrusions and formation. Formation of skarn in the contact zone of intrusions and limestone, marble. The main ore body under the control of the rock of diorite, granite porphyry and carbonate contact zone,which are layered, stratiform, lenticular. Useful elements are of Cu and Au. ore texture are of four main categories,which are crystallzation texture, metasomatic texture, solidsolution texture and supergene structure, according to origin, crystallzation texture, metasomatic texture, solidsolution texture are the main structural types, structure of ores according to the genetic classification of ore are the formation of contact metasomatism and hydrothermalism. The main ore minerals are Magnetite, chalcopyrite, azurite, bornite, chalcocite and pyrite. The major gangue minerals are Garnet, wollastonite, chlorite, epidote, diopside, actinolite, calcite, quartz and chalcedony. The country rock alteration mainly characterized by Contact alteration and hydrothermal alteration, developed hornfelsization, marbleization, skarnization, sericitization, silication, epidotization, chloritization, carbonation, albitization, argillization, among them, hornfelsization, skarnization, marbleization and silication are major.The rock has comparatively lower SiO2(52.92%～79.21%,the most is60%～65%,average (63.64%) and higher A12O3(10.43%～16.49%, average15.23),higher alkali (w(Na2O+K2O):4.86%～7.15%),w(Na2O)/w(K2O) chang-eable ratio (0.26～2.26),weak Eu anomalies and weak Ce anomalies, comparatively rich in incompatible element, such as Rb、Th、K、Ce, while low in Ba、Ta、Nb、Ti. The characteristics show the granite is metaluminous-weak peraluminous calc-alkaline Ⅰ-type granite, source region provenance may be basic basaltic element,formed in the continental marginal arc of active continental margin which connected to the plate subduction, the production of the migmatization of deep crustal material meltdown and mantle source basic magma.Ore-bearing rockmass with Zircon SHRIMP U—Pb dating yielded ages of112.0±2.3Ma(after Qu Xaoming and Xin Hongbo,2006) for the deposit. And Bangong-Nujiang oceanic basin began to subduct at166.4±2.0Ma (Qu Xaoming et al.,2009) in Shiquanhe-Gaize subduction zone. After the Large-scale subduction, subduction zone began to mature,and the structural environment turned into the subduction of active continental margin. Lead to form the granitic rocks of the Gaerqiong area.The formation of skarn deposits in the contact area of the acidic intrusive and carbonate rocks also areas in the vicinity. Combine geological and geochemical characteristics of granitoids, evolution of granitoids, analysis of metallogenic specialization and metallogenetic potentialit of granitoids, deposit characteristics and country rock alteration, looking for porphyry type Cu and Au deposits has great potential in the composite plutonat the North East of mining area, it is recommended to increase the input and research of geological work.