新疆西天山加曼特金矿床赋矿围岩年代学、地球化学及地质意义

Geochronology,Geochemistry and Geological Significance of Host Rocks in the Jiamante Gold Deposit,West Tianshan,Xinjiang

加曼特金矿床是西天山博罗科努多金属成矿带中的一个浅成低温热液金矿床。矿床赋存于晚古生代大哈拉军山组岩屑晶屑凝灰岩和花岗斑岩中。LA-ICP-MS锆石U-Pb同位素定年结果显示岩屑晶屑凝灰岩、花岗斑岩的成岩时代分别为(365.9±3.0)Ma和(362.3±4.3)Ma,结合上覆阿恰勒河组地层中维宪阶生物化石的时代,加曼特金矿的成矿时代被约束在362~331 Ma之间。矿区岩石地球化学分析结果表明:二者均为高钾钙碱性系列岩石,富集轻稀土、Th和大离子亲石元素(Rb、K),亏损Ba、Sr、高场强元素(Nb、Ta、Ti、P)和重稀土元素,具有同源性和岛弧岩浆岩的地球化学亲缘性。岩石形成于古准噶尔洋向伊犁—中天山板块俯冲的活动大陆边缘弧环境,主要是下地壳基性岩石部分熔融的产物,混合了少量洋底沉积物熔体交代地幔楔形成的幔源岩浆。

The Jiamante gold deposit is a typical epithermal gold deposit located in the Boluokenu polymetallic belt in the West Tianshan. It occurs in Late Paleozoic Dahalajunshan Formation mainly composed of crystal tuff and granitic porphyry. The LA-ICP-MS zircon U-Pb dating yielded a weighted average age of （365. 9 ±3.0） Ma for crystal tuff and （362.3 ±4. 3 ） Ma for granitic porphyry. The mineralization age of the Jiamante gold deposit could be constrained between 362 Ma and 331 Ma based on geochronological work in the study and considering the fossils of the Visean period in Lower Carboniferous Aqialehe Formation. Geochemical analysis results indi- cate that these magmatic rocks show high K calc-alkaline characteristics with enrichment in LREE, Rb, Th, K, and depletion in Sr, Ba, HREE, Nb, Ta, Ti and P. It suggests that crystal tuff and granitic porphyry have the characteristics of arc magmatic rocks. Crystal tuff and granitic porphyry were generated due to the southward subduction of the Junggar Ocean beneath the Yili-Middle Tianshan plate. They were likely derived from partial melting of mafic lower crust, with involvement of mantle-derived magma interacted with subducted sediments.