蒙西斑岩型铜钼矿地质地球化学特征及其对东准噶尔琼河坝岩浆岛弧构造属性的制约
Geological and geochemical characteristics of the Mengxi Cu-Mo deposit and its constraint to tectonic setting of the Qiongheba magmatic arc in eastern Junggar, Xinjiang
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摘要: 蒙西铜钼矿床位于东准噶尔北塔山-琼河坝岛弧带东段琼河坝大花岗岩基北接触带，具有矿化蚀变类型多样、构造应力破裂-充填脉体发育、及不同组分脉体垂向分带等特征，为形成于断裂构造背景下的斑岩型铜钼矿床，闪长玢岩与二长花岗斑岩为成矿斑岩。琼河坝地区以花岗岩为主体的岩体均为钙碱性系列岩石，富Pb、K、Sr、U、Th和Zr，贫Rb、Nb、Y、Ta、Yb与Ti，轻稀土富集，(La/Yb)N值介于3.1与15.5之间，在Rb-Y+Nb、Nb-Y、Rb-Ta+Yb与Ta-Yb图中位于VAG（火山岛弧花岗岩）区，与安第斯山火山岩具相似的微量稀土元素分配结构，为形成于大陆地壳构造背景下的岛弧型岩浆岩，其原始岩浆成分包含大陆下、中与上地壳的组分、并与安第斯山岛弧火山岩平均成分相当。蒙西铜钼矿床形成年龄为411Ma，蒙西矿区的闪长玢岩与二长花岗斑岩形成于晚志留纪-早泥盆纪。这意味着北塔山-琼河坝斑岩铜矿带可能是南蒙古欧玉陶拉盖（Oyu Tolgoi）斑岩铜矿带的西延。琼河坝地区以花岗岩基为代表的岩浆岩带为古生代大陆岛弧岩浆岩带，是形成与寻找斑岩铜矿的有利地区。Abstract: The Mengxi Cu-Mo deposit located north to the contact zone of Qiongheba granite batholith at the eastern segment of Beitashan—Qiongheba arc, eastern Junggar, is characterized by strong alternation, development of fracture-filled veins, and vertical zoning of veins with various mineral composition, and is kind of porphyritic Cu-Mo deposit strong affected by fault structures in the ore district. Diorite porphyries and feldspar porphyries are ore-forming porphyry in the Mengxi Cu-Mo deposit. Granite in the Qiongheba area are calc-alkaline, and characterized by high Pb, K, Sr, U, Th and Zr, low Rb, Nb, Y, Ta, Yb and Ti, enriched LREE with (La/Yb)N value from 3.1 to 15.5. All the 22 analyzed intrusive samples have plots in the VAG (volcanic arc granite) domain in diagrams of Rb-Y+Nb, Nb-Y, Rb-Ta+Yb and Ta-Yb, and similar trace element and REE spiders with that of continental arc volcanic in Andes. These granite were production of continental arc magmatism with a composition containing component from the upper, middle and lower continental crust and equal to the average of continental arc volcanic rocks in Andes. Result of Re-Os dating shows that both the molybdenite and Cu-Mo deposit in the Mengxi area were formed at about 411Ma BP, the diorite porphyries and feldspar porphyries in the Mengxi ore district and granite in the Qiongheba area were possible formed at latest Silurian- earlist Devonian. This indicates that Yemaquan-Beitashan- Qiongheba porphyries and porphyry copper mineralization belt is most likely the western extending of the the Oyu Tolgoi Silurian-Devonian porphyry copper mineralization belt. The granite belt in the Qiongheba area, as a part of Paleozoic continental arc magmatic belt, is a potential target for porphyritic Cu deposit.
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Key words:
- Mengxi Cu-Mo deposit /
- Re-Os dating /
- Element geochemistry /
- Magmatic arc /
- Tectonic setting /
- Eastern Junggar
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