新疆包古图斑岩铜矿中性复式岩体的同化混染作用

包古图斑岩铜矿位于新疆西准噶尔地区东南部,是一大中型斑岩铜矿床,赋存于包古图中性复式岩体中。包古图中性复式岩体是由早期闪长岩株和晚期闪长玢岩脉组成,以前者为主;该岩体侵位于下石炭统包古图组酸性火山-沉积岩中。对包古图闪长岩株及其围岩进行岩相学、岩石主量和微量元素地球化学及Sm-Nd同位素地球化学等方面进行研究。结果表明:闪长岩株由(石英)闪长岩(含少量辉长岩)、似斑状(石英)闪长岩及少量斜长花岗斑岩组成;其岩石是由偏基性的中性岩浆结晶(分异)作用及岩浆与酸性围岩同化混染作用形成的。同化混染作用的程度不同,则形成不同的岩石:①岩浆直接结晶作用形成辉长岩;②岩浆结晶(分异)作用和少量同化混染作用形成(石英)闪长岩和似斑状(石英)闪长岩;③强烈的同化混染作用形成斜长花岗斑岩,斑岩基质主要由混入岩浆的围岩细碎屑经重结晶作用形成,斑晶是晚于基质结晶的"晚生斑晶"。总之,岩浆与围岩的同化混染作用是包古图岩体的重要成岩作用。

Contamination and Assimilation of the Intermediate Complex in the Baogutu Porphyry Cu Deposit,Xinjiang

Baogutu porphyry Cu deposit located in the southeast of West Junggar Area,Xinjiang, which is a large-medium size deposit,is associated with a Late Carboniferous intrusive complex that is emplaced into Lower Carboniferous Baogutu Formation which consists of the felsic volcano sedimentary rocks.Baogutu intermediate complex includes the early-stage diorite stock in the majority and late-stage diorite porphyry dikes.Petrography,geochemistry of major and trace elements and Sm-Nd isotope of diorite stock and their wall rocks in Baogutu were studied.The results indicate that diorite stock consists of minor gabbro and plagiogranite porphyry excepting for dominant weakly porphyritic diorite and quartz diorite;they are formed by the contamination and assimilation of magma and felsic wall rock excepting for the crystallization of partial basic＆amp;nbsp;intermediate magma. The different rocks are resulted from the variable contamination and assimilation of magma.Gabbro is formed directly by the magma crystallization;the weakly porphyritic diorite and quartz diorite are formed by the magma crystallization with minor contamination and assimilation; the plagiogranite porphyry is formed by the dominant contamination and assimilation,and the matrix is formed by the recrystallization of fine-grained fragments from the wall rock which mixed into magma,and phenocryst called “late-forming phenocryst”is later than the crystallized matrix.In general,the contamination and assimilation of magma and wall rock play an important role in the formation of Baogutu rock.