深源岩浆作用与江西德兴大型矿集区成矿关系

RELATIONSHIPS BETWEEN THE DEEP SOURCED MAGMATISM AND METALLOGENY IN DEXING DENSELY ORE DEPOSITED AREA, JIANGXI PROVINCE, CHINA

德兴大型矿集区范围约长 2 0km、宽 10km ,已发现 3个大矿田 13个矿床和许多矿点。赣东北深断裂带控制了区域构造演化、岩浆活动和成矿作用。德兴矿集区的形成是构造—岩浆—成矿统一的地质作用的结果。深源岩浆作用对大规模多金属成矿有决定性的影响。中 新元古代海相火山喷发营造了双桥山群成矿建造———矿源层。中生代Ⅰ型花岗岩浆活动对大规模多金属成矿的制约主要有 5个方面 :⑴供给Cu、Pb、Zn、Au、Ag等成矿金属元素 ;⑵产生成矿热流体 ;⑶提供成矿热驱动力 ;⑷营造成矿空间 ;⑸激活围岩“矿源层”中的成矿物质参与成矿。

large ore fields including 13 ore deposits and a large number of ore occurrences are clustering in Dexing densely ore deposited area, which is 20 km long and 10 km wide The regional tectonic evolution, magmatism, as well as the metallogeny are controlled by the NE trending Jiangxi deep seated fault belt The formation of Dexing densely ore deposited area is the result of a unified geologic process of tectonism, magmatism and metallogensis. The large scale polymetallic mineralization is mainly controlled by the deep sourced magmatism The Precambrian and Mesozoic magmatisms were closely related to mineralizations The ore bearing formations and source beds of Shuangqiaoshan group with a thickness of 15 km of the Meso Neoproterozoic age were formed by submarine volcanic eruptions The large scale marine intermediate-basic volcanic eruptions produced a great quantity of spilite (basaltic)-keratophyre (andesitic) volcanics and pyroclastic rocks which would have carried abundant Cu, Mo, Pb, Zn, Au and Ag from upper mantle and lower crust to the upper crust The concentration of ore forming elements in these horizons suggests that they could be the source beds The large scale regional Ⅰ type granitoids were formed in the Mesozoic Petrological study supports the following model: The magma was originated from basic “amphibolite gabbro” at the deep crust (depth>27km), in which 40% magma with granodiorite composition was melted from the lower crust and partially assimilated by the “sial sphere” material in upper crust during the magma rising and evolved into the magma enriched in K 2O and H 2O The rock in magma source area contains a great quantity of Cu, Mo, Pb, Zn, Au and Ag, as well as the minerals abundant in H 2O such as amphibole and micas The sialic upper crust is the basement of Shuangqiaoshan Group and is also enriched in Cu, Pb, Zn, Au, Ag and minerals abundant in H 2O such as chlorite and sericite Consequently, the composition of the magma emplacing into the shallow crust was more baundant in ore forming elements and H 2O The constraints of I type granite in Mesozoic to the metallogeny are at least in five aspects: (1) supply ore forming metal elements such as Cu, Pb, Zn, Au and Ag; (2) supply hydrothermal fluids; (3) supply heat energy; (4) provide space for ore deposits; (5) activate the ore forming materials from adjacent rocks and prompt mineralizations