与新西兰北韦斯特兰巴里汤侵入岩体有关的热液蚀变和白钨矿化(英文)

HYDROTHERMAL ALTERATION AND SCHEELITE MINERALISATION ASSOCIATED WITH THE BARRYTOWN PLUTON,NORTH WESTLAND, NEW ZEALAND

侵入奥陶纪下部硬砂岩和页岩的‘S’型巴里汤黑云母花岗岩体在接近其原始顶板位置出露地表。该岩体从富黑云母的边缘至酸性的核部呈内部分带现象。影响很大一部分岩体的弱弥漫型热液蚀变由三种有明显区别的类型组成:早期绿磐岩化(绿泥石-绢云母±斜黝帘石、榍石)集中于北西-南东走向的、当时尚有余温的岩体核部上方,而其后的中性泥质蚀变(高岭石、伊利石-电气石)发育于顶板接触带附近,这是由于捕获和凝聚酸性挥发分造成的。石英-电气石脉及与其有关的云英岩边(花岗岩中的石英-白云母-金红石,变质沉积岩中的石英-白云母-电气石)仅见于绿磐岩的中央斜黝帘石-榍石部分,并且明显地晚于后者生成。它们含有少量的白钨矿和很少的黑钨矿、锡石、辉钼矿和黄铜矿。在黑云母蚀变过程中,丰富的钛相矿物可能在原地捕获岩浆的锡和钨,这阻碍了有效的淋滤和矿石的富集。

The 'S' type Barrytown biotite granite pluton which intrudes Lower Ordovician greywacke and shales is exposed noar its original roof level. The pluton is internally zoned from a biotite-rich margin to an acid core. Mild pervasive hydrothermal alteration which affects much of the pluton comprises 3 distinct varieties: early propylitic alteration(chlorite-sericite±clinozoisite, sphene) was concentrated above the NW-SE trending, residually warm pluton core, while later intermediate argillic alteration (kaolinite, illite-tourmaline) developed in the vicinity of roof contacts due to trapping and condensation of acid volatiles. Quartz-tourmaline veins and associated greisen selvedges (quartz-muscovite-rutile in granite, quartzmuscovite-tourmaline in metasediments) are restricted to, and apparently pcstdate, the central clinozoisite-sphene part of the propylitic zone, and contain minor scheelite and rare wolframite, cassiterite, molybdenite and chalcopyrite. Abundant secondary Ti-phases may have held magmatic Sn, W in situ during alteration of biotite, preventing effective leaching and potential ore concentration.