福建李家坊金矿区火成岩岩体锆石U-Pb年龄、地球化学特征及其地质意义

福建李家坊金矿为何宝山矿田近年新发现的中型金矿床,矿区内广泛发育火成岩岩体,然而,由于缺少对其岩浆活动时限及地球化学特征的研究,各类岩体与金矿化的关系尚不明确。针对这一问题,文章通过全岩主微量元素分析和LA-ICP-MS锆石U-Pb定年及微量元素测试,约束李家坊金矿床内火成岩岩体成岩年龄,并讨论了其地球化学特征。研究表明,矿区内加里东期赋矿围岩及其U-Pb年龄分别为:含白云母花岗岩为(432.2±3.9)Ma、含白云母正长伟晶岩为(438.7±4.6) Ma、含白云母碱长花岗岩为(424.5±3.1) Ma、黑云母花岗岩为(444.4±2.7) Ma及(446.6±7.1) Ma。其中黑云母花岗岩具有高w(P₂O₅)(0.15%)和低w(Na₂O)(2.66%)特征,A/CNK=1.07,属过铝质、高钾钙碱性、高分异S型花岗岩,在板内褶皱后造山伸展环境中由前寒武纪基底变质岩发生深熔作用形成。此外,矿区内首次获得燕山期存在岩浆活动的证据,钾长花岗岩和花岗斑岩年龄分别为(133.2±0.8) Ma和(135.6±3.1) M...

Zircon U-Pb age, geochemistry characteristic and its geological significance of igneous rock in Lijiafang gold deposit, Fujian

Lijiafang medium-sized gold deposit is newly discovered in Hebaoshan ore field, Fujian Province in recently years. Igneous rocks are widely developed in Lijiafang ore field. However, the relationship between these intrusions and gold mineralization is unknown due to the lack of study on magmatic activity time and geochemical characteristics. Based on the analysis of whole-rock major and trace elements, LA-ICP-MS zircon U-Pb dating and trace element analysis, this paper constrains the diagenetic age of igneous rocks in the Lijiafang gold deposit, and then discuss the geochemical characteristics of them. The result shows that the Caledonian host rocks are composed of muscovite-bearing granite, muscovite-bearing syenite pegmatite, muscovite-bearing alkali feldspar granite and biotite granite, which U-Pb ages are (432.2±3.9) Ma, (438.7±4.6) Ma, (424.5±3.1) Ma, (444.4±2.7) Ma and (446.6±7.1) Ma), respectively. The biotite granite belongs to the peraluminous, high potassium, calc-alkaline, and highly differentiated S-type granite, with A/CNK=1.07, high w(P₂O₅) (0.15%), and low w(Na₂O)(2.66%) values, was explained to form by the deep melting of Precambrian basement metamorphic rocks in the orogenic extensional environment after intraplate folding. Igneous rocks formed in Yanshanian have also been found for the first time in Lijaifang gold deposit, including moyite and granite porphyry, which has zircon U-Pb ages of (133.2±0.8) Ma and (135.6±3.1) Ma. The geochemical property of the former is A/CNK=0.80, FeO^T/MgO=8.55, Ga/Al=3.09, AKI=1.08, w(Zr+Nb+Ce+Y)=294.4×10^-6, and A/CNK=0.99, FeO^T/MgO=6.59, Ga/Al=2.68, AKI= 0.98, w(Zr+Nb+Ce+Y)=317.8×10^-6 of the later. Both belong to metaluminous high potassium calc-alkaline differentiation I-type granite, and formed under the extensional environment caused by the slab rollback of Paleo-Pacific Plate to Eurasian Plate. Combined with the large-scale Mesozoic gold mineralization events in South China and our unpublished Re-Os age data of molybdenite (~130 Ma), the Yanshanian igneous rocks may be the concealed ore-forming rocks.