黔西南板其卡林型金矿床方解石REE、Fe、Mn元素特征及其对找矿的指示意义

REE, Fe and Mn Contents of Calcites and Their Prospecting Significance for the Banqi Carlin-type Gold Deposit in Southwestern China

板其金矿床是黔西南卡林型金矿矿集区内的重要组成部分,是中国发现的第一个卡林型金矿床。方解石是其最主要的脉石矿物,按形成时间可分为成矿前、主成矿期、成矿晚期、成矿期后四种类型。各类型方解石无论野外产状、物性标型特征还是微量元素地球化学特征均不一致。四种类型方解石相比较,成矿前方解石稀土元素总量最高(ΣREE=29.70～40.10μg/g),最富集轻稀土元素(LREE/HREE=1.96～3.03),具有最大正Eu异常(δEu=3.83～5.02),无明显Ce异常(δCe=1.02～1.05);主成矿期方解石稀土元素总量相对较低(ΣREE=10.76～15.53μg/g),最富集重稀土元素(LREE/HREE=0.11～0.23),Eu异常(δEu=0.73～1.20)与Ce异常(δCe=0.88～1.25)均不明显;成矿晚期方解石稀土元素总量最低(ΣREE=2.82～4.34μg/g),与主成矿期方解石相似,具有重稀土元素富集特征(LREE/HREE=0.26～0.86),具有弱的负Eu异常(δEu=0.67～0.83)及负Ce异常(δCe=0.55～0.81);成矿期后方解石稀土元素总量相对较低(ΣREE=6.92～10.91μg/g),轻稀土元素富集(LREE/HREE=1.83～2.34),弱负Eu异常(δEu=0.72～0.74)与中等负Ce异常(δCe=0.41～0.50)。此外,成矿期方解石Fe、Mn元素含量明显高于非成矿期方解石,而且方解石Fe+Mn含量与LREE/HREE比值具有明显负相关关系,说明板其金矿床方解石富集重稀土元素与其所含的Fe、Mn元素有关。对方解石各种标型特征的研究,将为滇黔桂卡林型金矿找矿勘查提供重要手段。

The Banqi gold deposit is one of the important Carlin-type gold deposits in the southwestern Guizhou Carlin-type gold district, and it is the first deposit of the type found in China. As the major gangue mineral in this deposit, calcite can be divided into four types based on their formation time： pre-mineralization, main metallogenic epoch, late stage of mineralization, and post-mineralization. All types of calcites have distinct features such as field occurrence, physical typomorphic characteristics and trace elements characteristics. The pre-mineralization calcites have the highest REE contents（∑REE=29.70–40.10 μg/g）, which are characterized by the most enriched LREE（LREE/HREE=1.96–3.03）, a distinct positive Eu anomalies（δEu=3.83–5.02）, and almost no Ce anomalies（δCe=1.02–1.05）. The calcites of the main metallogenic epoch have relatively low REE contents（∑REE=10.76–15.53 μg/g）, and are characterized by the most enriched HREE（LREE/HREE=0.11–0.23）, almost no Eu（δEu=0.73–1.20） and Ce anomalies（δCe=0.88–1.25）. The calcites of the late stage of mineralization have the lowest REE contents（∑REE=2.82–4.34 μg/g）, and are characterized by enriched HREE（LREE/HREE=0.26–0.86）, weakly negative Eu（δEu=0.67–0.83） and Ce anomalies（δCe=0.55–0.81）, which are similar to those of the calcites of the main metallogenic epoch. The post-mineralization calcites have relatively low REE contents（∑REE=6.92–10.91 μg/g）, characterized by enriched LREE（LREE/HREE=1.83–2.34）, weakly negative Eu anomalies（δEu=0.72–0.74） and moderately negative Ce anomalies（δCe=0.41–0.50）. In addition, the Fe and Mn contents of ore-forming stage calcites are obviously higher than that of the calcites unrelated to mineralization, and negatively correlated with LREE/HREE ratio, which illustrates that the HREE concentrations of calcites are controlled by the incorporation of Fe and Mn. Thus, it will provide an important exploration indicator for the Yunnan-Guizhou-Guangxi Carlin-type gold deposits through the study of typomorphic characteristics of calcite.