胶东邢家山地区燕山早期钼钨成矿母岩锆石U-Pb年龄及其意义

对从幸福山花岗岩中挑出的岩浆锆石进行了LA-ICP-MS分析,得出了由15个点组成的加权平均值为(157±2)Ma的年龄。此15个测试点均处于岩浆锆石的振荡环带上,且此年龄与邢家山钼钨矿辉钼矿Re-Os年龄一致,代表该花岗岩的结晶年龄。本次测试所得到的另外2组捕获锆石年龄(2798±13)Ma和(2250±18)Ma暗示该岩浆源区可能存在的新太古代-古元古代侵入岩基底,(230±6)Ma则可能暗示着该区存在三叠纪的岩浆活动。中生代以来(190~110 Ma),中国东部构造岩浆活动特征较为一致,与之相对应存在多期成矿作用。胶东地区广泛出露的玲珑花岗岩与幸福山花岗岩岩石地球化学特征及年龄基本一致,可能该区也存在着大规模的钼多金属成矿作用,只是大部分为后期构造抬升所剥蚀,邢家山钼钨矿是保存下来的代表。也说明,栖霞—福山地区中生代以来剥蚀程度相对较小,矿床保存条件较好,故应重视该区中浅成矿床(斑岩-矽卡岩型、卡林型、造山型浅成矿床等)的寻找。

Accurate zircon U-Pb dating of Early Yanshanian molybdenum-tungsten mother rocks in Xingjiashan area of Jiaodong Peninsula and its significance

Abstract: This paper presents the magma zircon LA-ICP-MS U-Pb isotopic dating results of the Xingfushan granites. The weighted mean age (157±2 Ma) was obtained from 15 test points on the oscillatory zones. Inferred from the same test positions and the coincident dating result with Re-Os isotopic age of molybdenite from the Xingjiashan molybdenum-tungsten deposit, the granites here crystallized in this period. The other two captured zircons from the same assay at the separate age of (2798±13) Ma and (2250±18) Ma imply possible existence of Neoarchean-Paleoproterozoic intrusive basement, whereas No. 7 point at the age of (230±6) Ma implies possible Triassic magmatic activity. The consistent features of the tectono-magmatic activities in eastern China since Mesozoic (190?110 Ma) produced the corresponding varied metallogenesis here. The common granites of Linglong and Xingfushan units in Jiaodong Peninsular share almost the same geochemical features and ages, suggesting that this area might have hosted large-scale molybdenum polymetallic metallogenesis. Under heavy regional denudation by late tectonic uplifting, the left Xingjiashan molybdenum-tungsten deposit typically shows less denudation in Qixia-Fushan area since Mesozoic and better metallogenic condition, so more importance should be attached to the prospecting for hypabyssal deposits (porphyry-skarn, Carlin and organic hypabyssal deposits) here.