川西滴痴山高分异花岗岩与辉钼矿的成因联系

Genetic Linking between Pegmatite⁃Type Veined Molybdenum Deposit and Dichishan Highly Differentiated Granite in West Sichuan

为查明川西滴痴山高分异花岗岩与伟晶岩型脉状钼矿的成因联系,开展了岩石地球化学、锆石U-Pb及辉钼矿Re-Os同位素年龄研究.结果显示,滴痴山花岗岩体具高的SiO_(2)(72.95%~75.44%)、Al2O3(13.93%~14.99%)和A/CNK(1.11~1.25),为高钾钙碱性和过铝质系列,富集高场强元素Th、Ce、Zr、Sm及大离子亲石元素Rb,亏损高场强元素Hf、Yb及大离子亲石元素Ba.滴痴山花岗岩中锆石LA-ICP-MS U-Pb加权平均年龄为201.9±0.8 Ma,锆石log fO_(2)=-15.40±2.89,△FMQ=-0.40±2.89,为低氧逸度环境;伟晶岩中辉钼矿Re-Os年龄为188.6±4.8 Ma.滴痴山花岗岩为燕山早期高分异S型花岗岩,形成于后碰撞环境,为松潘‒甘孜地块南缘岩石圈从挤压向伸展构造体制的转换期.松潘‒甘孜地区伟晶岩型脉状辉钼矿的发现,为川西九龙地区钨钼矿找矿勘探工作拓宽了思路.

To find out the genetic linking between the Dichishan highly differentiated granite and pegmatite vein molybdenum deposit in West Sichuan,the petrogeochemistry,zircon U-Pb and molybdenite Re-Os isotopic age were studied in this paper.Samples from the Dichishan granite show variable SiO_(2)of 72.95%-75.44%and are characterized by Al2O3(13.93%-14.99%)and high aluminum saturation index(A/CNK=1.11-1.25).They are high K calc-alkaline and peraluminous series,enriched in high field strength elements Th,Ce,Zr,Sm and large ion lithophile element Rb,depleted in high field strength elements Hf,Yb and large ion lithophile element Ba.The molybdenite Re-Os weighted mean age is 188.6±4.8 Ma(MSWD=0.90),which is consistent with LA-ICP-MS zircon U-Pb dating results of the granite yielded 206Pb/238U ages of 201.9±0.8 Ma.The oxygen fugacity parameter of zircon shows its low oxygen fugacity(log fO_(2)=-15.40±2.89,△FMQ=-0.403±2.89).It proposes that the Dichishan granite batholith was emplaced in a syn-collisional setting,formed in early Yanshannian highly fractionated S-type granite.It represents the transition period of tectonic system from lithospheric compression to extensional in the southern margin of the Songpan-Garze Block.The discovery broadens the perspectives about mineral exploration in Jiulong region and its surrounding areas in West Sichuan.