ABSTRACT

Processed tailings in the Mixed tailings impoundment at the Macraes gold mine built up a sedimentary pile up to 100 m thick between 1990 and 2013. The tailings consist of sand-dominated fluvio-lacustrine sediments with fine (cm scale) bedding and have a mineralogical stratigraphy that reflects changing mine processes. Most of the tailings (>90%) consist of silicate minerals discarded from the flotation system throughout that time. The deepest tailings (1990–1993) have the lowest contents of sulphides as these were extracted and deposited separately. Between 1993 and 1999, tailings with up to 0.5 wt% sulphide sulphur (as pyrite and arsenopyrite) were deposited. Introduction of a pressure oxidation system in 1999 caused a substantial decrease in sulphide minerals and a parallel increase in ferric oxyhydroxide, ferric sulphate, and ferric arsenate compounds in which trace metals are dispersed. Some primary scheelite reacted during pressure oxidation conditions to form ferric tungstate compounds. Processing of auriferous sulphide concentrate from Reefton, western South Island, from 2007 introduced stibnite to the ore stream, and this was readily oxidised to form insoluble As-bearing ferric antimonate.

摘要

Macraes 金矿混合尾矿库中的加工尾矿在 1990 年至 2013 年间形成了一个厚达 100 m 的沉积堆。尾矿由以沙为主的河湖沉积物组成，具有细（厘米级）层理，具有矿物地层这反映了不断变化的采矿过程。大部分尾矿（>90%）由在此期间从浮选系统丢弃的硅酸盐矿物组成。最深的尾矿（1990-1993 年）的硫化物含量最低，因为它们是单独提取和沉积的。在 1993 年至 1999 年间，沉积了高达 0.5 wt% 硫化物硫（如黄铁矿和毒砂）的尾矿。1999 年引入压力氧化系统导致硫化矿物大量减少，而羟基氧化铁、硫酸铁、以及其中分散有痕量金属的砷酸铁化合物。一些初级白钨矿在压力氧化条件下反应形成钨酸铁化合物。从 2007 年起，对来自南岛西部 Reefton 的含金硫化物精矿进行加工，将辉锑矿引入矿石流，这很容易被氧化形成不溶性的含砷锑酸铁。