黑龙江金厂铜金矿床火山岩锆石U-Pb年代学及地质意义

ZIRCON U-Pb CHRONOLOGY AND ITS SIGNIFICANCE FOR VOLCANIC ROCKS FROM JINCHANG CU-AU DEPOSIT , HEILONGJIANG PROVINCE

金厂铜金矿床东部及外围广泛出露一套中酸性火山岩系,岩性为流纹质、英安质凝灰岩及晶屑凝灰岩。作为火山岩主体的流纹质凝灰岩,其w(SiO2)为66.32%～75.56%,w(Al2O3)为12.09%～15.64%,总碱量w(Na2O+K2O)为6.40%～7.91%,且CaO>MgO,Na2O>K2O,Al2O3/(CaO+K2O+Na2O)<1.1,属中酸性准铝质钙碱性岩石系列。火山岩样品TY-6的锆石谐和年龄为(210.4±1.6)Ma;TY-7的锆石谐和年龄为(210.0±1.9)Ma,显示火山岩成岩时代为印支晚期。结合岩性特征,说明研究区火山岩应归属于三叠世罗圈站组(T3l)。火山岩岩石化学特征表明研究区火山岩为地壳部分熔融产物。罗圈站组火山岩可能标志着区域构造由兴蒙造山结束并向环太平构造转换。而金厂铜金矿床成矿时代为118.6Ma,说明金丰度较高的罗圈站组火山岩(210Ma左右)其原始岩浆可能存在着金的预富集,且可能为金厂铜金矿床成矿提供部分物质。但二者不具有直接的成因联系。

A suite of intermediate-acidic volcanic tuff occurs in the east and outskirt of Jinchang Cu-Au deposit.It has variable w（SiO2）（66.32%～75.56%）,w（Al2O3）（12.09%～15.64%）contents and higher CaO and Na2O contents than MgO and K2O,with w（K2O＋Na2O）varying from 6.40%to 7.91%and Al2O3/（CaO＋K2O＋Na2O）〈1.1respectively.The zircons from the sample TY-6yield a concordia age of（210.4±1.6）Ma whereas the zircons from the sample TY-7 yield concordia age of（210.4±1.9）Ma,indicative of the volcanic activity of late Indosinian and consistent with volcanic rock of late Triassic Luoquanzhan Group（T3l）.It is showed that the volcanic rocks of studied area belongs to the Luoquanzhan Formation（T3l）and resulted from partial melting of crust.The volcanic rocks of Luoquanzhan Formation are considered as a regional tectonic transition from the end of Xing′anling-Mongolian orogeny and to the initial of Pacific plate subduction to the Eurasia plate.Since the Jinchang Copper-gold deposit has a mineralization age of 118.6Ma,it is likely that the preconcentration of gold element occurs in primary magma which formed Luoquanzhan Formation and provided part of ore material to the Cu-Au mineralization.However,they do not have direct genetic relationship.