桂东北苗儿山-越城岭东北部界牌钨-铜矿区成矿岩体锆石U-Pb年龄及华南加里东期成矿分析

界牌W-Cu矿床产于苗儿山-越城岭复式岩体东北部斑状黑云母花岗岩与灰岩接触带的矽卡岩中,是苗儿山-越城岭复式岩体矿集区最大的矽卡岩型W-Cu矿床。矿区出露的主要岩体为斑状黑云母花岗岩及后期浅色花岗岩体,矿区外围则大面积出露斑状黑云母二长花岗岩。矿化产于斑状黑云母花岗岩与灰岩接触带矽卡岩,及斑状黑云母花岗岩中灰岩捕虏体矽卡岩化带中。黑云母花岗岩发育花岗岩型钨矿床成矿早期常见的钠长石化、云英岩化及从岩体至外接触带蚀变矿物组合显示形成温度逐渐降低。这些现象表明斑状黑云母花岗岩与矿床具有紧密成因联系。本文获得矿区斑状黑云母花岗岩、斑状黑云母二长花岗岩和浅色花岗岩体锆石LA-ICP-MS U-Pb年龄分别为:422±11 Ma,428±7 Ma,410±7 Ma,表明界牌W-矿床及区内主要岩体均形成于加里东期。本文的同位素年龄及前人报道的苗儿山-越城岭矿集区和华南加里东期与花岗岩有关矿床同位素年龄表明苗儿山-越城岭矿集区W-Mo-Cu矿床成矿主要发生在加里东期和印支期,U矿成矿主要发生在燕山期,华南在加里东期发生了分布广泛、成矿元素组合多样的与花岗岩有关的成矿事件,有很好的找矿前景,今后应加强华南加里东期矿床的找矿工作。

Zircon U-Pb Ages of Ore-bearing Intrusions in Jiepai W-Cu Deposit Northeastern Guangxi and Implication on Caledonian Mineralization in South China

The Jiepai deposit is the largest W-Cu deposit in the Miaoershan-Yuechengling area that is rich in metallic ore resources. The W-Cu orebodies are hosted in the skarns at the contact between the porphyritic biotite granite and limestone. The intrusions in the Jiepai deposit consist mainly of porphyritic biotite granite and late stage leucogranite dike. Porphyritic biotite quartz monzonite outcrops widely around the Jiepai ore field. The ore-bearing porphyritic biotite granite underwent albitization and greisenization. The temperatures estimated by the alteration mineral assemblages decrease from the inner to outer contact zone, indicative of a genetic link between the porphyritic biotite granite and W-Cu mineralization. Zircon LA-ICP-MS U-Pb ages of the porphyritic biotite granite, porphyritic biotite quartz monzonite, and leucogranite dike are 422±11 Ma, 428±7 Ma, and 410±7 Ma, respectively. Our zircon U-Pb ages indicate the major intrusions and related W-Cu mineralization in the Jiepai area were formed in the Caledonian period. Based on the zircon U-Pb ages and previous works on the deposits around the Miaoershan-Yuechengling ore rich domain and the other deposits in the South China, it is suggested that the W-Mo-Cu deposits around the Miaoershan- Yuechengling ore rich domain were formed mainly in the Indosinian and Caledonian periods, while the U deposits were mainly formed in the Yanshanian period. The Caledonian granite-related ores are widespread in South China and have diverse element associations, such as W-Cu, W, W-Mo, Mo, Au, and Fe-Cu-Pb-Zn. Therefore, the potential of the Caledonian granitoid related ore deposits are much greater than previously considered, and thus more attention should be paid to the Caledonian granitoids in the future ore prospecting in South China.