Study On Genesis For Typical Deposits Of Southwest Duolong Ore Field, Tibet

Duolong ore field is located in Gaize county, and it’s tectonic location is on the north of west Bangong Lake-Nujiang Metallic Belt, and on the south of Qiang Tang Bolck. In this paper, we choosed Dibaonamugang deposit and Nadun deposit form southwest of Duolong ore field as the research objects, and respectively choosed drill DNZK6428 from Dibaonamugang and drill NDZK0001 from Nadun for petrographic,mineragraphy and geochemical studies, to explore the geneses of the two deposits. The main conclusions are listed below.(1) Dibaonamugang is a typical high-sulfidation epithermal deposit. The host rock of Dibaonamugang deposit is granodiorite-porphyry, which is high potassium calc-alkaline to calc-alkaline peraluminous rock. The metallic mineral assemblage of Dibaonamugang contains sulfide minerals as pyrite, chalcopyrite, bornite, covellite, galena, sphalerite, enargite, luzonite, digenite, chalcocite, tennantite etc and native gold. Drill DNZK6428 can be divided into 5 alteration zones form top to deep: silified zone, kaolinite zone, argillization zone, anhydrite-calcite zone and propylitic zone. The alteration mineral assemblage of Dibaonamugang contains quartz, kaolinite, alunite, pyrophyllite, chlorite, epidote, sericite, muscovite and carbonate minerals etc.(2) Nadun deposit is a low-sulfidation epithermal deposit. The host rock of Nadun deposit is sub-granodiorite-porphry, which is formed by granodiorite-porphyry magma intrued into the early andisite pipe and is high potassium calc-alkaline to shoshonite peraluminous rock. The metallic mineral assemblage of Nadun contains pyrite, chalcopyrite, bornite, digenite, magnetite, emplectite, wittchenite, electrum bismuthine, bismite, galena, cinnabar, siderite etc. Drill NDZK0001 can be divided into 2 alteration zones from top to deep: silica- argillization zone, mica-carbonation zone. The alteration mineral assemblage of Nadun deposit contains quartz, muscovite, sericite, cholrite, calcite, dolomite and other clay minerals.(3) The metallogenic process of Dibaonamugang deposit can be described as follow. Step one, magma enplacement: granodioritic magma derived from magma chamber intruded into shallow surface and formed granodiorite-porphyry, along with a small amount of pyritization. Step two, hydrethermal minerallazation: magmatic hyrothermal form deep upwelled into the former granodiorite porphyry along the magma path, carrying metals to deposit and form sulfate alteraton as well.(4)The metallogenic process of Nadun deposit can be described as follow. Step one, magma enplacement: granodioritic magma derived from magma chamber intruded into an early volcano pipe, and formed sub granodiorite porphyry, along with a certain degree of pyritization. Magma below the pipe formed fine-grained granodiorite porphyry with a certain degree of minerlazation. Step two, hydrethermal minerallzation: hydrethermal quartz dikes moved along former fracture structure and carried some granodiorite breccias; these dikes deposited in the sub granodiorite porphyry and formed the main metallogenic zone of Nadun.(5)Duolong ore field is a typical porphyry--high sulfidation epithermal--low sulfidation epithermal ore field. For other porphyry metallogenic belt, we should use this combination of porphyry-epithermal deposits in mine prospecting work; For the outer space of some porphyry deposit, we should work more on explanation of epithermal deposit.