论辽宁锦西杨家杖子杂岩体的岩浆成因演化及成矿作用

ON THE MAGMA GENERATION, EVOLUTION AND MOLYBDENUM MINERALIZATION OF THE YANGJIAZHANGZI COMPLEX, JINXI, LIAONING PROVINCE

杨家杖子杂岩体中的二长闪长岩代表一种母岩浆,它是燕山早期库拉板块向欧亚板块下俯冲所产生的,并汇聚上升的安山质岩浆。粗粒似斑状二长花岗岩、细粒似斑状二长花岗岩和(碱长)花岗斑岩是二长闪长岩浆在7km深、弱还原环境、氧逸度为10^(-8)～10^(-10)Pa、1200°～1250℃的岩浆房中经结晶分异作用的派生物。以后,这些岩浆相继上侵,定位于2.5km深处。由这些岩浆岩侵入体所引起的镁夕卡岩、钙夕卡岩和岩浆期后酸性热液淋滤蚀变非常发育。只有来自细粒似斑状二长花岗岩和(碱长)花岗斑岩岩浆、富含Mo的酸性热液沿着裂隙侵入夕卡岩中,在240～330℃时,才形成Mo矿床。此种酸性热液也沿着裂隙侵入细粒似斑状二长花岗岩和(碱长)花岗斑岩中,而形成细脉浸染Mo矿床。因此,杨家杖子Mo矿床属于斑岩-夕卡岩型。

Mesozoic monzodiorite in Yangjzazhangzi represents a mother magma which was an andesitic magma generated by the subduction of the Kula plate underneath the Eurasian one, and then assembled and uplifted to a high level. The coarse-grained pseudoporphyritic monzogranite, the fine-grained pseudopophyritic monzogranite and the (alkali-feldspar) porphyry granite are derivatives of the monzodiorite magma due to crystallization differentiation in the magma chamber at a depth of about 7km, under weak reduction conditions, at 1200°～1250℃ and 10^(-18) to 10^(-16) of oxygen fugacity. These magmas were emplaced to a depth of about 2kin successively. The magnesio-skarn, calcioskarn and postmagmatic acidic leaching alteration caused by these igneous intrusive bodies are well developed there. Only the acidic hydrothermal solutions derived from magmas which have formed the fine-grained pseudoporphyritie monzogranite and (alkali-feldspar)granite porphyry, with high content of Mo(120ppm) invaded skarns along fissures to from Mo-ore deposit at 240°～330℃. Such an acidic hydrothermal solution has invaded the fine-grained pseudoporphyritic monzogranite and (alkali-feldspar)granite porphyry along fissures also, to form dissiminated and fine veined Mo-mineralization. Thus the Yangjiazhangzi Mo-ore deposits belong to a porphyry-skarn type.