Geological Characteristics And Genesis Discussion Of The Tawenchahanxi Fe-polymetallic Deposit In Qimantage Area, Qinghai Province

The Tawenchahanxi Fe-polymetallic deposit is located in the southeast section(probably 300 degrees direction) of the Qimantage Hill in Qinghai province, which is about 200 km from the northwest of Geermu city. In recent years, it is another medium-sized Fe-polymetallic deposit after the Shaqiu, Changshan and Niukutou deposits, which contains more than 40 million tons of proven iron ore resources. The orebody and ore-forming rock mass are covered by Quaternary eolian sand. The geotectonic position of mining area is located in the North Qimantage Early Paleozoic magmatic arc belt, which is also located in the north of Nalinggele fracture in the East KunLun. The deposit is located among east longitude 92°31’-92°52’,north latitude 36°55’-37°00’,with a total area about 100km2.Through analysis the geological characteristics, the mineralization alteration zoning of the deposit and geochemical characteristics of the ore-forming rock mass, this article is in order to find out the geological genesis of the deposit, mineralization, ore controlling factors and prospecting model. By comparing with other deposits, in the larger area establish the main type of ore deposit and summarize the metallogenic regularity, so as to guide the mineral exploration and practice. Finally, related to the relationship of tectonic magmatic mineralization in Qimantage area and the geological characteristics and genesis of the deposit, we get the main research results are as follows:(1)Carding summed up the conclusions that in Early Triassic approximately during(242~239 Ma),the western of East-Kunlun orogenic belt(Qimantage area) is during the transition stage which is in the end of the oceanic crust subduction to the began of the continental crust collision,while translate into stretch after the collision stage during(237~204 Ma). At the same time the mantle-derived magma invasion and crust-mantle mixing action has occurred on a large scale.Especially, the Middle-Late Triassic(210~237Ma) granitoids are predominant and most closely related with mineralization.(2)By the LA-ICP-MS zircon U-Pb dating, this paper gets the porphyritic granodiorite in the ZK25408 borehole,(236.12±1.2 Ma) Ma, which represent the magmatic crystallization age,belonging to the Triassic(T2). Accordancing with the previous scholars’ results yield a 40Ar-39 Ar plateau age of(230.7±2.0 Ma)and an isochron age of(229.9 ±3.5 Ma)by measuring the muscovite separated from skarn magnetite ore, which prove the magmatism’s contribution to the mineralization.(3)Find out in the Tawenchahanxi Fe-polymetallic mine granite diorite porphyry may be the I-type granite series with the characteristics of peraluminous, high K calc-alkaline.It was enriched in HFSE and LREE,while poor in LILE and HREE. The rare earth patterns of rocks/chondrite show the right deviation with the character of negative Eu.(4)Middle and late Triassic corresponds to the last tectono-magmatic-metallogenic cycle, meanwhile is a main metallogenic period of the late Qimantage region. NWW direction of regional deep faults control the distribution of the main intrusion and mineralization area, Secondary fault with occurrence significant ore body. Tawenchahanxi Fe-polymetallic deposit is a typical fault and magmatism of common control ore type with the characteristics of skarn type ore deposit and the hydrothermal vein type deposit.(5)Tawenchahanxi Fe-polymetallic deposit experienced stage of skarn and quartz-sulfide. Among them, the skarn stage are subdivided into early stage and late stage of skarn and degradation of alteration stage while the quartz-sulfide stage are subdivided into early stage(iron-copper sulfide phase) and late sulfide phase(phase lead-zinc sulfide).(6)Ore structure, mineral composition and the characteristics of the wall rock alteration, indicating deposit metallogenic temperature and element has zonality: Near the contact zone according to the distances from the center of the intrusion from near to far SiO2 and Fe2O3, Al2O3 content from high to reduce gradually, the CaO content from low to increase. Higher temperature mineral mainly distribute in the inner contact zone zone, while the high-temperature mineral group distribute in the outer contact zone.(7)Inductive speculated that the main source of sulfur in the ore of Tawenchahanxi Fe-polymetallic deposit is a deep source of magma, accompaniing with different levels of the crust sulfur; The main lead has a mantle-derived lead source having the possibility of mantle source and shell source causes.And all this suggest that the ore-forming hydrothermal for late magmatic hydrothermal mixed with deep circulation of groundwater of different degrees.