湘西南地区基性——超基性岩型硫化镍矿找矿前景

Prospecting Prospect of Basic-ultrabasic Rock Type Nickel Sulfide Deposits in Southwestern Hunan Province

湘西南地区处于扬子板块与华南褶皱系拼接带内,深大断裂贯穿全区,幔源岩浆活动强烈,青白口纪(雪峰期)基性—超基性岩成群成带分布。在通道陇城开展镍矿找矿工作,获取了丰富的找镍信息,首次发现了隐伏含镍矿化带,厚61.66 m,全镍(TNi)平均品位为0.1%。通过研究陇城基性—超基性岩带岩石岩相、地球物理、地球化学、镍矿化特征,并与广西宝坛地区已知的含矿岩体进行了对比分析。结果表明:(1)超基性岩为引起磁异常的起因,含镍超基性岩具有"三高一低"(高磁性、高密度、高极化率、低电阻率)的物性组合特征,是寻找镍矿的重要物探标志;(2)独立的辉绿岩w(∑REE)、w(La)/w(Lu)值为边缘相辉绿岩的2～3.5倍,地表辉绿岩w(∑REE)、w(La)/w(Lu)值较低(分别为50×10-6左右、(20～30)×10-6),为寻找镍矿的地球化学标志;(3)镍矿受高分异岩体控制,超基性辉橄岩、橄榄岩带为含镍矿化带,往深部可能出现贯入型矿体。在上述分析的基础上,进一步研究认为,湘西南地区今后镍矿找矿工作思路为:率先对陇城地区已知的镍矿化带进行深部钻探验证,通过开展地面磁测工作筛选找矿靶区,结合稀土测试工作甄选岩脉(体),以重、磁、电物探测深组合手段预测定位镍矿体。

Southwestern Hunan Province lies in the junction belt of Yangtze Plate and South China fold system,with deep and large faults running through the whole area,mantle-derived magma activity is strong,and the distribution of basic-ultrabasic rock in Qingbaikouan strata(Xuefengian)are grouped and zoned.Prospecting work of nickel deposit is carried out in Longcheng in Togndao County,abundant prospecting information is obtained,concealed nickel mineralized belt with the thickness of 61.66 m and average TNi grade of 0.1%is discovered.By studying the petrography,geophysics,geochemistry and nickel mineralization characteristics of Longcheng basic-ultrabasic rock belt,and comparing them with the known ore-bearing rocks in Baotan Area in Guangxi Province.The study results show that:(1)ultrabasic rock is the cause of magnetic anomalies,the nickel-bearing ultrabasic rock have the physical combination characteristics of"three high and one low"(high magnetism,high density,high polarizability and low resistivity),which is the important geophysical indicators for the prospecting of nickel deposit;(2)w(∑REE)and w(La)/w(Lu)values of the independent diabase are 2~2.5 times of marginal diabase,w(∑REE)and w(La)/w(Lu)values of surface diabase are both lower than others,w(∑REE)is about 50×10^-6,w(∑REE)is(20~30)×10^-6,it can be regarded as geochemical indicator for the prospecting of nickel deposit;(3)the nickel deposit is controlled by high differentiation pluton,the ultrabasic pyroxene peridotite and peridotite zones are nickel mineralized zones,and penetrated orebodies may appear in the deep part.Based on the above discussion results,further analysis results indicated that the prospecting ideas of nickel orebodies in Southwestern Hunan Province can be summarized as:the known nickel mineralization belt in Longcheng Area can be firstly verified by deep drilling engineering,prospecting target area can be delineated by ground magnetic survey work,based on rare earth testing results to select the dikes(bodies),therefore,metallogenic prediction and location of nickel orebodies can be done effectively by means of the combination method of gravity,magnetic and electrical geophysical sounding.