蒙古国查干苏布尔加大型铜-钼矿床地质特征及成因

The Geology and Ore-forming Mechanism of the Tsagaan Suvarga Large-size Cu-Mo Porphyry Deposit in Mongolia

查干苏布尔加斑岩铜钼矿床位于西伯利亚板块南缘近东西向和北东向深大断裂所夹持的南蒙古构造岩浆带内,容矿围岩二长花岗斑岩与花岗闪长斑岩主量元素高SiO2(64.69×10-2~73.42×10-2),高Al2O3(15.33×10-2~18.35×10-2),贫MgO(0.13×10-2~0.56×10-2),微量元素Sr二长花岗斑岩略低(144×10-6~175×10-6),花岗闪长斑岩表现为高Sr(样品>300×10-6,476×10-6~720×10-6),二者均低Y(Y<18×10-6,2.21×10-6~10.20×10-6),低Yb(Yb<1.9×10-6,0.30×10-6~1.48×10-6),高Sr/Y(Sr/Y>20,21.8~63.52),稀土元素特征为亏损重稀土,无明显负铕异常,(87Sr/86Sr)i=0.70154~0.70397,(143Nd/144Nd)i=0.512290~0.512600,εNd(t)为+2.4^+8.5,二长花岗斑岩和花岗闪长斑岩均具有埃达克质岩特征,但二长花岗斑岩与花岗闪长斑岩主、微量和稀土元素又存在一定差别,它们可能是岩浆不同演化阶段的产物。通过年龄测定,获得辉钼矿Re-Os等时线年龄为(370.0±5.9)Ma,二长花岗斑岩锆石SHRIMPU-Pb加权平均年龄为(365.7±3.6)Ma,铜钼矿形成时代与二长花岗斑岩形成时代相近,均形成于晚泥盆世。铜钼矿床与二长花岗斑岩、花岗闪长斑岩紧密共生,矿区范围内二长花岗斑岩与花岗闪长斑岩多被蚀变并矿化,表明二长花岗斑岩、花岗闪长斑岩与铜钼矿化存在密切的时空关系,为铜钼成矿提供了主要成矿物质和流体来源。

The Tsagaan Suvarga large-size Cu-Mo porphyry deposit is located in the southern Mongolia tectonic-magmatic island arc belt between the NE-trending and EW-trending deep faults on the southern margin of the Siberian plate.The copper-molybdenum mineralization is hosted in the monzogranite porphyry and granodiorite porphyry that intruded early Devonian intermediate-mafic volcanic and volcanoclastic rocks.This paper has provided major and trace element compositions of ore-hosting monzogranite porphyry and granodiorite porphyry in the Tsagaan Suvarga large-size Cu-Mo porphyry ore district：the major compositions are SiO2 64.69×10^-2～ 73.42×10^-2,67.50×10^-2 on average;Al2O3 15.33×10^-2～18.35×10^-2,16.88×10^-2 on average;MgO 0.13×10^-2～0.56× 10^-2,0.16×10^-2 on average;trace element compositions are Sr 96.70×10^-6～612×10^-6,382.78×10^-6 on average;Y 2.21×10^-6～10.20×10^-6,7.46×10^-6 on average;Yb 0.30×10^-6～1.48×10^-6,1.07×10^-6 on average;Sr/Y 21.8-63.52,48.12 on average;rare earth element compositions are ΣHREE 1.63-7.06 μg/g,LREE/HREE 4.96～10.74,（La/Yb）N 5.57～13.68,δEu 0.87～1.09,0.98 on average;and Sr-Nd isotope compositions are ^87Sr/^86Sr initial value 0.70154～0.70397,0.70322 on average;^143Nd/^144Nd initial value 0.512290～0.512600,0.512459 on average;εNd（t） ＋2.4～＋8.5,＋5.7 on average.These data show that the granodiorite porphyry and monzogranite porphyry has characteristics of adakitic rocks which are spatially and temporally associated with copper molybdenum mineralization.According to precise isotopic age studies,the Re-Os dating of molybdenite samples separated from the ore body yielded the isochron age of（370.0±5.9）Ma,and zircon SHRIMP U-Pb dating of the monzogranite porphyry yielded weighted average age of（365.7±3.6）Ma,suggesting that mineralization took place in Late Devonian,coeval with that of the monzogranite porphyry.The Cu-Mo ore bodies are associated with the monzogranite porphyry and granodiorite porphyry in spatial distribution,and almost the whole monzogranite porphyry and granodiorite porphyry experienced mineralization and alteration in the ore district.According to the above evidence,the adakitic magma provided primary ore-forming materials and fluids,the ancient Mongolian oceanic plate conducted rapid low-angle subduction under the northern margin of the old Siberia plate in a high-temperature,high pressure and water-rich environment,and the adakitic magma formed from direct melting of the oceanic plate,with the simultaneous precipitation of Cu,Mo,Au,Ag and other metallogenic elements.During the upward migration of adakitic magma,the ore-forming metallic elements were extracted from the mantle wedge,and these elements rapidly ascended to the shallow position along with the adakitic magma.With the variation of the physical-chemical conditions,the metallogenic elements underwent unloading,precipitation and enrichment,and ultimately formed the ore deposit.