Keyan Xiao, Chinese Academy of Geological Sciences (China)
Jianhua Ding, Chinese Academy of Geological Sciences (China)
Juxing Tang, Chinese Academy of Geological Sciences (China)
Xiaohua Zhang, Chinese Academy of Geological Sciences (China)
It's very important for assessment the endowment of undiscovered mineral resources. There are some methods discussed by some authors such as tonnage-grade model (DA .Singer 1986). Two quantitative assessment methods has been discussed and compared in this paper.
Geochemical methods have been generally used in mineral resource quantitative assessment. Most of them were based on geochemical data and geological factors such as tectonic, strata, etc. were less taken into account. Improvement of this method has been made in this paper.East Tianshan area was selected as an example to show the progress. During the geologic history in East Tianshan area, several times plates collision has occurred which resulted in complex tectonic process, long perdurability of minerogenesis, multi-minerogenesis and overlay of several metallogenic types. Accordingly, the cause of geochemical anomalies is complex and using geochemical data as only rule to divided massif units will bring on bias. In the paper, heterogeneity of geochemical element distribution has been taken into account when calculate the threshold. After integrated study, we finished a zoning map of lithology formation, on which seven subareas has been divided. Quaternary strata has been subtracted because of great distortion of geochemical value. Threshold of every subarea has been calculated individually. Processing like this, some errors can be shield which can help to get more reasonable estimate result.
The second method of quantitative assessment is grade-tonnage model method which is based on Monte Carlo Simulation. Grade, tonnage, undiscovered deposits number are three important variables. In this paper, a new method of estimating the possible deposit number has been put forward. Three permissive belts were delineated due to minerogenetic tectonics environment and minerogenetic epoch. Eighty-five perspective tracts were delineated due to geological assessment information, geochemical concentration center and geophysical anomaly. There are three known porphyry copper deposits in East Tianshan working area. Nonlinearity network method, which is suitable for quantitative assessment without known deposit model or few models, was used to subdivide the perspective areas into three classes: A is the most targets, B is middle and C is less. The number of perspective areas of class A is for the deposit number with 50 probability. Similarly, number of class B is for deposit number with 25 probability and C is for 10 probability.
The calculate results of two methods were compared in the paper. The difference is within a limit of allowable error.