吕宋岛弧西缘浅成低温热液成矿作用——以拉拉布金矿床为例

拉拉布脉状金矿床是西必塔矿集区最典型的矿床,而西必塔矿集区脉状浅成低温热液型金矿是近年来发现的最具经济潜力的金矿床之一。金矿赋存于中新世—更新世马林丹群火山岩中,该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,并受到安山玢岩侵入。该火山岩可分为上、下段两段。下段由安山质熔岩、英安岩、凝灰岩组成,上段为火山角砾岩和凝灰质角砾岩。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。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30~200 m之间。金的富集有4个阶段(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。

Epithermal mineralization in the Western margin of the Luzon arc:Lalab gold deposit

The Lalab gold deposit is the most typical deposit in the Sibutad ore-concentrated area,and this area is regarded as the most promising economically feasible vein-type epithermal gold mineralization in the Western margin of the Luzon arc.The gold deposit occured in Pliocene-Pleistocene volcanic rocks.The volcanic rocks scattered as island-shaped in the east of the active Sindangan-Cotabato-Daguma Lineament belt.The host rocks are the Melinda Volcanic,consisting of lower and upper members,which are both intruded by andesite porphyry.The lower member is made up of andesite flows,dacite tuff and tuffite,whereas volcanic breccia and tuff breccia occupy the upper member.Lalab gold deposit is characterized by distinct hydrothermal alternation in adnesite flow.Therefore it belongs to adularia-sericite type.Gold was precipitated from reduced,near-neutral pH solutions in a surficial environment due to mixing of boiling hydrothermal fluid.Gold concentration in Lalab deposit is related with(l)pre-breccia wall rock alteration,(2)hydrothermal brecciation,(3)post-breccia wallrock alteration,and(4)gold mineralization.Prolific gold zones occur between 30 m below sea level and 200 m above sea level.