铅同位素在矿产资源评价中的应用--以甘肃省鹰嘴山金矿区为例

Application of Pb isotopes to evaluation of mineral resources:A case study of Yingzuishan gold deposit,Gansu Province

文章在铅同位素示踪的有关理论和隐伏矿预测方法的基础上,以甘肃省鹰嘴山金矿区为例,提出了利用铅同位素进行隐伏矿深度、形态与资源量预测的方法。在鹰嘴山金矿区共采样122个,分析结果显示：①地表铅同位素勘探线剖面的V1与V2值在矿体及其相邻蚀变带均出现了明显的负异常,并接近区域地壳平均值,且显示出一个明显的变化规律,即自东至西,矿体的V1与V2值存在着从高到低的规律变化。②V2平均值从122线的43.57（蚀变带上）到46线下降至35.67,标志着矿体的揭示深度从东到西存在着由浅至深的变化规律。从116线到90线,矿体V2平均值从40呈线性下降至36.62,表明116线以东进入隐伏区,90-116线达到矿体出露的中上部,而80线以西出露的矿脉已代表了矿体的下部,并趋向于尾部。③从46线向东到116线,地表可见矿体向下的延深变大,从200m增大到1049m,说明矿体整体西高东低,向东侧伏（隐伏）。④矿区总平均隐伏系数RS为3.68,46线至116线,矿体的预测资源量为42.5t,表明鹰嘴山金矿床应为大型-特大型金矿床。

A new method is proposed to predicate the depths, shapes and mineral resources of blind ore deposits based on previous studies of the Pb isotopes tracing and a case study of the Yingzuishan gold deposit in Gansu Province. According to the requirements for prognosis of blind deposits by using Pb isotopes and detailed field geological work on the ground surface, the authors collected representative samples in the peripheral areas of the Yingzuishan gold deposit so as to determine regional background values of Pb isotopes and construct the target indices for ore exploration in these peripheral areas. Meanwhile, based on the requirements for establishment of a profile for chemical prospecting in the ore district by using Pb isotopes, the authors collected representative samples of both rocks and ores for prediction of the depths and reserves of blind ores in this deposit. The major conclusions and working progresses are summarized as follows： （1） Distinct negative anomalies of both V1 and V2 values for the Pb isotope-based chemical prospecting profile at the ground surface were found in both the ore district and its adjacent alteration zones, and the anomaly values are close to the average levels of the earth＇ s crust in the study area. From the 7 profiles for chemical prospecting in the ore district, the V1 and V2 values for the ore deposits show regular decrease from the east to the west. （2） V2 average values decrease from 43.57 at line 122 （above the alteration zone） to 35.67 at line 46, which suggests that the revelation depth of the ore deposit increases regularly from the east to the west. The V2 average values for the ore deposit decrease linearly from 40 at line 116 to 36.62 at line 90, demonstrating that the area to the east of line 116 is the target area for blind ores, the area between lines 90-116 is the middle to upper part of the ore deposit, while the area to the west of line 80 represents the lower part, which is close to the bottom of the ore deposit. （3） From line 46 extending eastward to line 116, the ore bodies exposed at the ground surface show a increasing trend in the extension depth, i.e., from 200 m to 1 049 m. This indicates that the depth of the entire ore body is lower in the east than in the west, symbolizing its eastward inclining trend （in n hidden way） （4） Rs, the average hidden coefficient, of the ore district averages 3.68 in general, and the predicted reserves for the ore bodies between line 46 and line 116 are 42.5 tons. Therefore, the Yingzuishan gold deposit is likely to be a large to superlarge gold deposit, implying the existence of huge mineralization potentials and the great value for further exploration and development. Drill holes arranged by Gansu Bureau of Exploration and Development of Geology and Mineral Resources all intersect economic gold ore bodies, showing that the method discussed in this paper is effective in the prognosis of blind deposits.