东天山土屋-延东斑岩铜矿带埃达克岩及其与成矿作用的关系

The relationship between ore-forming processes and adakitic rock in Tuwu-Yandong porphyry copper metallogenic belt, eastern Tianshan mountains.

土屋-延东铜矿带位于东天山晚古生代大南湖增生岛孤带,容矿岩石斜长花岗斑岩侵入于岛弧火山岩区。通过对容矿围岩化学组成的研究表明,主量元素SiO2、Al2O3和MgO的含量分别为64.37％-72.28％、17.77％～17.71％和0.55％-1.35％,微量元素Y、Yb和Sr的含量分别为4.42—11.1(μg/g),0.38—0.87(μg/g)和619—738(μg/g),LREE为富集型和Eu为正异常,这些特征反映斜长花岗斑岩为埃达克质岩。本区埃达克岩与铜矿化存在密切的时空关系,铜矿形成时代与埃达克岩相近,形成于早石炭世,而火山岩形成于泥盆纪。铜矿与埃达克岩紧密共生,矿区范围埃达克岩多被蚀变并铜矿化。同位素地球化学特征反映,埃达克质岩浆为成矿提供了主要的物质和流体来源。进一步研究表明,岛弧火山岩与具埃达克岩性质的斜长花岗斑岩形成于不同的地质过程。本区中基性-中酸性的岛弧火山岩是由于大洋板块俯冲到深部,因脱水作用使板片之上的地幔楔发生部分熔融而形成的。而埃达克岩是俯冲到深处具MORB性质的板片在一定的物理化学条件下发生部分熔融后直接侵位于近地表而形成的。

Tuwu-Yandong porphyry copper deposits lies in East Tianshan Mountains, eastern section of Central Asia orogenic belt. The copper deposits occur in the Paleozoic Dananhu island arc on the northern margin of Tarim plate. The copper mineralization is hosted in plagiogranite porphyry intruded into early Devonian intermediate to mafic volcanoclastic rocks. This paper reported major and trace elements compositions of ore-hosting plagiogranite porphyry in Tuwu-Yandong ore belt. The compositions of SiO2 (64.37% 72.28 %), Al2O3 (14.77% similar to 17.71 %), MgO (0.55% - 1.35%), Y (4.42 - 11.1 mug/g), Yb (0.38 similar to 0.87 mug/g), Sr (619 similar to738 mug/g) and positive Eu anomalies indicate that the plagiogranite porphyry shows characteristics of adakitic rock. The adakitic rocks are spatially and temporally associated with copper mineralization: the mineralization age is early Carboniferous, a little younger or same as that of the adakitic rocks; the copper ore bodies are associated with the adakitic rocks in spatial distribution; and almost all the adakitic rocks were altered and mineralized in the ore area. The study on isotopic geochemistry indicates that the ore-forming materials and fluids came mainly from the adakitic magma. We suggest that the volcanic rocks and adakitic rocks in the island are were formed during different geological processes. The former was formed in partial melting of mantle wedge on the subducting slab, which the later was formed in direct melting of oceanic plate.