云南三江地区典型金矿床吨位-边界品位曲线特征

Tonnage-cutoff grade curves for the typical gold deposits in the Sanjiang area,Yunnan,SW China

吨位-平均品位-边界品位曲线是矿床评价的重要参考,也是理解成矿过程的一个窗口。本文借助吨位-平均品位-边界品位分形模型,选取我国三江地区典型金矿床的局部地段矿体——北衙万硐山磁铁矿-赤铁矿型矿体、镇沅冬瓜林浸染状低温硫化物型矿体、大龙潭氧化硫化物型矿体以及勐满热水塘强硅化泥化蚀变的热泉型矿体;热水塘主要为低品位矿石,而其它三个矿床品位相对较高;分别计算了四个金矿床的吨位-边界品位曲线,并分析其特征。文章提出矿化分散指数(MDI),将其定义为Ko=-ΔO/ΔGc,Km=-ΔM/ΔGc(ΔGc为两个边界品位之差,ΔO与ΔM分别为相对应的矿石量与金属量之差);Ko与Km值越小,表明空间中金属分布相对分散。文中分析的四个金矿床的曲线均是低边界品位区间的矿化分散指数较高(MDI1,即Ko1,Km1),高边界品位区间的矿化分散指数相对较低(MDI2,即Ko2,Km2);说明在不同类型金矿床中,高品位区间比低品位区间的金属空间分布更加分散。Ko1和Ko2由高到低依次为热水塘、大龙潭、万硐山和冬瓜林,Km1和Km2由高到低依次为热水塘、万硐山、大龙潭和冬瓜林。热水塘的矿化分散指数比其他三个矿床高,说明热泉型金矿成矿元素空间分布比较集中。

Tonnage-average grade-cutoff grade curves are important for mineral deposit evaluation and understanding ore-forming process.In this paper,based on the fractal models of tonnage-average grade-cutoff grade models,the curves in selected orebody area of the typical gold deposits,including magnetite-hematite dominated gold orebody at Wandongshan,disseminated low-temperature sulfides orebody at Donggualin,oxidized sulfides orebody at Dalongtan and hot-spring orebody with strong silicified-argillic alteration at Reshuitang in the Sanjiang area,Yunnan,SW China,are calculated.The Reshuitang deposit mainly contains low-grade ores,and the other three have relatively high-grade.The characteristics of the tonnage-cutoff grade curves are analyzed,in which the mineralized dispersion index（MDI） is put forward.The MDI is defined as the minus ratio of ΔO（difference between ore tonnages at two specialized cutoffs） to ΔGc（difference between the two cutoffs） and as that of ΔM（difference between metal tonnages at the two specialized cutoffs） to the ΔGc.The lower Ko or Km indicates that the metal distribution is relatively more dispersed in space.In the four analyzed deposits,their curves are consistently composed by a higher MDI segment in the lower cutoff range（named MDI1,i.e.,Ko1,Km1） and a lower MDI segment in the higher cutoff part（named MDI2,i.e.,Ko2,Km2）.It suggests that the metal is more dispersed in the high-grade range than in the low-grade one in different types of gold deposits.The Ko1 and Ko2 from high to low are Reshuitang,Dalongtan,Wandongshan and Donggualin deposits in turn,and the Km1 and Km2 from high to low are Reshuitang,Wandongshan,Dalongtan and Donggualin deposits.The greater MDI in Reshuitang deposit suggests the metal is more concentrated in this type of deposit.