冀北东坪似斑状花岗岩中石英斑晶成因及其流体包裹体研究

The Dongping giant gold deposit，situated in northern Hebei Province, was firstly found among the alkaline complex in China. The gold deposits in this surrounding area are usually recognized as alkaline rock-related gold deposits because of host rocks. However，geochronology shows that these gold deposits were formed during Jurassic, while the alkaline complex was formed during Devonian. The gold mineralization may be gold-vein quartz and gold-bearing altered rock types, and is also controlled by the shear zones. Porphyry-like granite was newly found in recent years, and is significant for understanding the origin of gold deposits in this area.. The aim of this research is to reveal gold mineralization in porphyry-like granite and its relationship with gold-quartz vein and gold-bearing altered types in the Dongping deposit by studying porphyry-like granite, quartz phenocryst, and fluid inclusions. The main research contents which will be carried on includes three aspects: 1) petrology of porphyry-like granite; 2) the origin of quartz phenocryst; 3)fluid inclusions in quartz phenocryst; 4) gold mineralization in porphyry-like granite; and 5) the relationship between fluid inclusions in quartz phenocryst and gold mineralization. . The distinguishing features and new ideas of this proposal includes three aspects. Fistly, the geological controlling conditions of ore-bearing porphyry-like granite will be concerned, which include the genetic relations with alkali complex and NEE-SWW trending shear zones. Secondly, the research will focus on quartz phenocryst in porphyry-like granite, and a varity of rock textures and various fluid inclusion types will be studied, so that the origin of quartz phenocryst, ore-forming fluid evolution and gold mineralization associated with the Dongping gold deposit can be understood. And the last, that how the gold minealization in porphyry-like granite is related with gold-quartz vein and gold-bearing altered rock types is also concerned in the proposal, which is conducive to understanding the origin of the Dongping giant gold deposit and regional prospecting.

通过对冀北东坪地区的含矿似斑状花岗岩、“石英似斑晶”及其流体包裹体的研究，查明似斑状花岗岩金矿化与东坪石英脉型、蚀变岩型金矿化的关系。主要研究内容有：1）似斑状花岗岩的岩石学；2）石英“似斑晶”的成因；3）“似斑晶”石英中的流体包裹体；4）似斑状花岗岩的金矿化；5）“似斑晶”石英中的包裹体与金矿化关系。项目特点和主要创新点包括：1）查明含矿似斑状花岗岩的控岩地质条件，与碱性二长岩杂岩体、NEE-SWW向剪切带构造的成因联系；2）以似斑状花岗岩的“石英似斑晶”为切入点，研究各种特殊的岩石结构和复杂的流体包裹体种类，探索石英似斑晶成因，结合东坪金矿的成矿流体特征，为区域金矿化的流体演化及成矿作用研究提供依据；3）揭示似斑状花岗岩金矿化与东坪石英脉型、蚀变岩型金矿化的成因联系，阐明这种在碱性杂岩体内产出的、与构造-热液叠加改造相关的金矿化对东坪特大型金矿成因及区域找矿的理论意义。

冀北东坪金矿外围近年来发现的似斑状花岗岩脉，呈NEE-SWW方向展布于碱性杂岩体中, 局部金矿化。查明似斑状花岗岩脉形成年代、石英似斑晶的成因，以及似斑晶石英中的流体性质及演化，对研究金矿成因和找矿方向有特殊意义。主要研究内容有：似斑状花岗岩的岩石学；石英似斑晶成因及其流体包裹体；似斑状花岗岩的金矿化；以及流体演化与金矿化关系。研究获得了似斑状花岗岩中，与海西期碱性杂岩有继承关系的岩浆残留锆石U-Pb年龄373.0±3.5Ma，热液改造锆石年龄142.02 ±1.2Ma，似斑状花岗岩中的钾长石Ar-Ar坪年龄144.27~148.17Ma，这些年龄与矿区南部燕山期钾质花岗岩浆的活动时代相当，证实似斑状花岗岩脉形成于晚侏罗世至早白垩世，与东坪金矿床的成矿密切相关。石英似斑晶内流体包裹体丰富，主要为盐水溶液包裹体，有时见富CO2包裹体和含石盐多相包裹体，熔体包裹体偶可见到。可分出3个世代，早世代包裹体的均一温度较高，为321℃-395℃，盐度19.0–5.1wt%NaCl。提出似斑状花岗岩脉是从含残浆的熔流体或超临界流体形成的，结合年代学依据，推测其形成与燕山期钾长花岗岩浆活动有关。建立了似斑状花岗岩脉与东坪金矿化的成因模式：1）早泥盆世至晚二叠世，西伯利亚板块与华北板块的碰撞导致广布的岩浆活动。中泥盆世东坪地区碱性岩浆侵入于中太古界崇礼群，形成水泉沟碱性杂岩体（SQG），构成了金的矿源体。2）三叠纪以来太平洋板块向西俯冲,引起中国东部强烈的花岗质岩浆活动。晚侏罗世至早白垩世上水泉（SSQ）钾质花岗质岩浆，侵入于碱性岩体和崇礼群，分离出熔流体（超临界流体）。3）具有高温、较高盐度和富含Si、K、Na的超临界流体，沿剪切构造带萃取了围岩碱性杂岩及部分崇礼群变质岩中的金，形成了NE-SW向展布的似斑状花岗岩脉和东坪等众多金矿床。项目获得的成果可为矿床成因研究和区域找矿提供理论依据。