长江中下游地区的矽卡岩交代柱特征与深部找矿

Characters of the Skarn Metasomatic Column in the Middle and Lower Reaches of the Yangtze River Region and Deep Prospecting

长江中下游地区是中国东部重要的铁、铜多金属成矿带,主要有矽卡岩型、层控矽卡岩型、斑岩型、矿浆型、玢岩型的铁、铜多金属矿床。在绝大多数金属矿床中广泛分布有钙质矽卡岩,根据矽卡岩交代柱特征可以把矽卡岩交代柱的形成分为三个阶段:首先是岩浆期-矽卡岩阶段,主要由钙铁石榴子石、辉石等矿物组成,其中含有熔融包裹体,均一法平均温度950～1 300℃。因为在熔融包裹体中见有石榴子石、辉石、方解石、硅灰石、石英、钙长石及玻璃和碳酸盐熔体等残留物,成分复杂多变,而且熔融包裹体中辉石和玻璃的化学成分,与邻区的火山岩中的辉石及玻璃相比MgO、CaO高得多,而K2O、Na2O少,两者明显不同,故仍应属于矽卡岩的矿物。该阶段常伴有磁铁矿化及富铁矿浆,形成矿浆型铁矿床。其次为早期碱性交代-矽卡岩阶段和酸性淋滤-矽卡岩阶段,主要为液相包裹体,亦含流-熔融包裹体,均一温度为150～580℃之间,根据液相包裹体分析成矿流体为H2O-NaCl-CO2型,成矿作用与沸腾关系密切,此阶段为本区铜、金多金属矿物沉淀期。总体分析,本区金属矿床应属透岩浆流体成矿体系。冬瓜山矽卡岩-斑岩型铜矿床和安庆铜矿床的成矿深度分别已达1 km以上和2.7 km(估算)。现今应重视矽卡岩和碱质蚀变(钾化和钠化)的广度和强度,可作为重要的深部找矿标志。

The middle-lower reaches of the Yangtze River region is an important metallogenic belt of iron, copper and polymetallic in eastern China. It include mainly skarn-type, stratabound skarn-type, porphyry-type, pulp-type, porphyrite-type iron and copper-polymetallic deposit in this region. Metal deposits are widely distributed in the calcareous skarn. And based on the characteristics of the skarn metasomatic column, the formation of the skarn can be divided into two stages： Fristly, magmatic-skarn stage, which mainly composed by the calcium-iron garnet, pyroxene, etc., containing melt inclusions, which homogenization temperatures are 950 - 1 300℃. There are garnet, pyroxene, calcite, wollastonite, quartz, calcium feldspar, glass and carbonate melt residue materials in the melt inclusions of which the composition are complex and changeable, i.e. The MgO and CaO of pyroxene in melt inclusion of volcanic rock in adjacent areas are higher than that of glass, while the K2O and Na2O less than that of glass. So it should belong to the product of the skarn. Magnetite mineralization and rich ore slurry are usually accompanied in this stage, which forms a slurry-type iron ore deposits. Second stage is the early alkaline metasomatism-skarn and acid leaching-skarn stage. The inclusions in it are mainly fluid inclusions and flow-melt inclusions. The homogenization temperatures is 150- 580℃. According to the liquid inclusions analysis, the mineralization fluid is H2O-NaCl-CO2-type, and mineralization is closely related with the boiling phase. This stage is precipitation period of copper, gold and multi-metal in this area. Generally, the metal deposits in this area should be permeable magmatic fluid ore-forming system. In the depth of skarn-porphyry copper deposit in Dongguashan （1 km） and copper deposit in Anqing （2.7 km, estimated）, we should pay attention to the breadth and intensity of the skarn and alkaline （potassium and sodium ）, which can be used as an important sign of deep prospecting.