菲律宾保和岛达瑙镍矿地质特征及成因探讨

菲律宾保和岛达瑙镍矿床位于西比克尔-东莱特岛(Western Bicol-Eastern Leyte)蛇绿岩带附近,矿体分布在超基性岩体顶部的褐铁矿层、腐泥土层中,与地表红棕色土壤的分布范围基本一致。层中硅镁镍矿较为发育,主要含镍矿物为镍绿泥石、暗镍蛇纹石。化学分析结果显示成矿物质来源于超基性岩;对矿区超基性岩、气候、地理位置、岩石破碎程度等特征进一步分析研究,认为该矿床的成因类型为风化壳淋积矿床。地壳抬升超基性岩接受风化,释放出Ni~2+。Ni~2+随地表水下渗至褐铁矿层下部的腐泥土层(风化岩石)中被蛇纹石矿物捕获,富集成矿。类质同象中的Mg~2+释放出来,由于本区地层渗透性好,Mg~2+至基岩处富集。一般而言,红土层下面的风化岩石含Ni最富。

Geological Characteristics and Preliminary Study to Genesis of Danao Nickel Deposit in Bohol, Philippine

Danao nickel deposit is located near the Western Bicol-Eastern Leyte ophiolite belt. Ore-bearing limonite and saprolite layers above ultramafic rocks consisted with red-brown soil where garnierite ores developed well. Chemical analysis showed that the mineralization source is ultramafic rocks; further analysis and study on the ultramafic rock, climate, geography, and degree of rocks fragmentation suggested the genesis type of deposit is weathering crust-eluvial type. According to the crust uplift, the ultramafic rocks weathered to release Ni2+ which was captured by the serpentines when infiltrated to the limonite and saprolite layers with surface water, isomorphied and then released Mg2+. Due to the high permeability, Mg2+ were enriched near the basement rocks, while Ni2+ serpentine was into the limonite and saprolite layers, precipitated down, and concentrated to mineralize.