色那金矿石英二长闪长岩锆石U-Pb年龄与地球化学特征及其对成矿背景的约束

Zircon U-Pb Age & Geochemical Characteristics of the Quartz Monzobiorite and Metallogenic Background of the Sena Gold Deposit in Duolong Metallogenic Concentrated Area,Tibet

色那金矿是西藏多龙矿集区内发现的一个浅成低温热液型金矿点，其成岩成矿时代一直缺乏精确的年代学约束。对该金矿石英二长闪长岩进行了LA—ICP—MS锆石U—Pb定年、主-微量元素分析和Sr—Nd同位素组成研究，首次获得了多龙矿集区色那金矿赋矿岩石的成岩时代。石英二长闪长岩LA—ICP—MS锆石U—Pb年龄为（122．0±1．8）Ma，代表岩浆的结晶年龄。石英二长闪长岩具低硅（57．26％～58．88％）、高铝（16．58％～17．50％）、富镁（2．65％～2．98％）特征，铝饱和指数（A／CNK）为0．93～1．09，富集轻稀土元素（LREE／HREE-6．28～7．25），8Eu为0．85～1．05，富集大离子亲石元素Rb、U、La、Sr、Sm，亏损高场强元素Nb、Ta、Zr、Hf等，相对于原始地幔具高Sr[（^87Sr／^86Sr）i=0．705023～0．705453]、低Nd[eNd（t）=-0．18～2．43]的同位素组成和古老的Nd同位素二阶段模式年龄（TDM2=0．78～1．03Ga），属于偏铝质-过铝质岛弧型花岗岩。多龙矿集区色那金矿早白垩世末岩浆活动与成矿作用很可能是班公湖一怒江洋向北俯冲诱发洋壳物质部分熔融，并有少量俯冲沉积物（3．1％～5．1％）和幔源岩浆参与部分熔融混合形成母岩浆，再经一定程度的分异结晶作用和接触交代作用而形成。

The Sena gold deposit recently discovered in Duolong metaltogenic concentrated area is an epithermal gold deposit. There is few high-precision petrogenic and metallogenic geochronological data. The zircon U- Pb dating, the major elements, trace elements and zircon Sr- Nd isotopic data of the ore- hosting quartz monzobiorite in Sena deposit are reported in this paper. Weighted mean U- Pb age of the Zircon from the quartz monzobiorite, （122. 0± 1. 8） Ma, can be regarded as the age of magmatic crystallization. The ore-hosting quartz monzobiorite in the Sena gold deposit is characterized by low SiO2 （ 57.26% to 58.88% ）, high A1203（16.58% to 17.50%）, high MgO （2.65% to 2.98%）, （A/CNK）- 0.93 to 1.09, rich in LREE （LREE/HREE=6.28 to 7.25）, Eu=0.85 to 1.05, meanwhile by high Rb,U, La, Sr, Sm contents, coupled with low Nb, Ta, Zr, Hf contents. Compared with primary mantle, the quartz monzobiorite in Sena gold deposit has respectively high Sr [-（ 87Srff6 Sr）i = 0. 705 023 to 0. 705 4531, low Nd[εNd （t） = -0.18 to 2. 431. The model age （TDM2 =0. 78 to 1. 03 Ga） indicates that the quartz monzobiorite belongs to the over aluminum granite. Authors suggest that the Early Cretaceous magmatism and mineralization be caused by crystallization differentiation and contact metasomatism of parent magma which consist of partial melting materials, few sediments and mantle derived magma.