青海野马泉铁锌矿床二长花岗岩锆石U-Pb和金云母Ar-Ar测年及地质意义

青海野马泉铁锌矿床地处祁漫塔格山与柴达木盆地之间的盆山结合部位,是矽卡岩型铁锌多金属矿床。矿体均呈隐伏?半隐伏状产出、具多期次强烈岩浆活动叠加等特征。长期以来,有关野马泉铁锌多金属矿床的成矿岩体和成矿时代众说纷纭,制约了对该矿床成因机制的认识及进一步的矿产勘查工作。本文基于详细的野外实地调查和矿床地质特征解剖,开展了成岩成矿年龄精测,探讨了成矿构造环境。铁锌矿体产于二长花岗岩与围岩地层的外接触带,发育石榴子石、透辉石、金云母、绿帘石等矽卡岩化作用。利用LA-ICP-MS锆石U-Pb法,获得成矿二长花岗岩的年龄为229.5±2.2 Ma(n=22,MSWD=1.3);采用Ar-Ar分步升温法获得与磁铁矿共生的金云母坪年龄为222.0±1.3 Ma(MSWD=0.41)、等时线年龄为222.4±2.5 Ma(MSWD=1.4),证实野马泉铁锌多金属矿床形成于晚三叠世,成矿岩体属过铝质、高钾钙碱性系列,为I-A过渡型花岗岩,具有高SiO_2,高K_2O/Na_2O,低P_2O_5,低Sr高Yb的特点。结合区域其他多金属矿床最新成岩成矿年代学数据,认为野马泉矿床形成于东昆仑地区海西?印支造山旋回晚期、由碰撞向后碰撞转换的地质构造环境。

Zircon U-Pb and Phlogopite Ar-Ar Ages of the Monzogranite from Yemaquan Iron-zinc Deposit in Qinghai Province

TheYemaquan iron-zinc deposit is a typical skarn-type deposit located in the border area between the Qimantage orogenic zone and the Qadam Basin. A few concealed or semi-concealed ore bodies have been explored in this deposit. However, the lack of information regarding the ages of ore-related granite and ore-formation restricts the understanding of the genesis and further exploration. U-Pb dating of zircons from the ore related monzogranite yielded an age of 229.5±2.2 Ma (n=22, MSWD=1.3), while Ar-Ar analysis of phlogopite associated with magnetite gave a plateau age of 222.0±1.3 Ma (MSWD=0.41) and isochron age of 222.4±2.5 Ma (MSWD=1.4). The dating results indicated that the Yemaquan Fe-Zn deposit was formed in the Middle to Late Triassic. The monzogranite rocks have high SiO2 contents, high K2O/Na2O ratios, low P2O5 contents and Sr/Yb ratios. Combining with the available petrogenetic and metallogenic ages and regional tectonic research works, it is suggested that the compression to extension transition during the Late Paleozoic to Early Mesozoic led to the formation of the widely distributed granitic intrusions and a large number of porphyry and skarn-type poly-metallic deposits in the Qimantage area.