菲律宾拉拉布金矿床围岩蚀变与成矿作用

从"景"、"场"、"相"、"床"4个等级体制观点出发,阐述了该金属成矿省成矿内部组成,观点新颖。金矿赋存于中新世-更新世马林丹群火山岩中,该群火山岩呈零星岛状散布于斯丹岗-哥塔巴托-大姑玛线性构造活动带(SCDL)的东部,并受到后期安山玢岩的侵入。安山玢岩具有埃达克岩性质,它的侵入对于后期的围岩蚀变和成矿作用起到重要的控制作用。拉拉布矿床的安山岩具有明显的热液蚀变,属于冰长石-绢云母型金矿化,认为金是在PH值近中性的浅表环境中由于热液沸腾并伴随流体的混合沉淀而成,通常富集于标高30~200m之间。围岩蚀变强度大,并有明显的分带规律,制约着金矿的形成。金的富集与下列地质事件相关:(1)形成角砾岩之前的围岩蚀变作用;(2)热液角砾岩的形成;(3)形成角砾岩后的围岩蚀变作用;(4)金矿形成。

RELATIONSHIP BETWEEN MINERALIZATION AND WALLROCK ALTERATION IN THE LALAB GOLD DEPOSIT, PHILIPPINES

Epithermal vein gold deposit is one of the most potential gold deposits discovered recently in the Sibutad ore district,Philippines.Thereinto,the Lalab large-scaled vein gold deposit is one of the most important epithermal gold deposits.Based on the four-grade ranking system in terms of tectonic background,geochemical-geophysical field,lithofacies and deposit,the structure of the Sibutad ore district was depicted in this paper.These epithermal gold deposits occur in the Pliocene-Pleistocene Lindan Group volcanic rocks intruded by andesite porphyrites,scattering over the east of the Sindangan-Cotabato-Daguma linear active zone.Geochemically,these andesite porphyrites are similar to adakite rocks.The intrusion of the andesitic magma is crucial to the epithermal gold mineralizaiton and its relative alteration.In the Lalab epithermal vein gold deposit,the alteration is pervasive and zoned.The alteration character indicates that the Lalab gold deposit belongs to the adularia-sericite subtype.It is suggested that gold was precipitated from neutral solutions induced by fluid boiling and mixing in the near-surface environment.The gold orebodies of the Lalab deposit occur at a range of depth from 30m to 200m below sea level.The following geological events are relevant to gold enrichment:(1)pre-brecciation alteration,(2)hydrothermal brecciation,(3)post-brecciation alteration,and(4)gold mineralization.