Abstract
Hierarchical or cascade resource estimation is a very common practice when building a geological block model in metalliferous deposits. One option for this is to model the geological domains by indicator kriging and then to estimate (by kriging) the grade of interest within the built geodomains. There are three problems regarding this. The first is that sometimes the molded geological domains are spotty and fragmented and, thus, far from the geological interpretation. The second is that the resulting estimated grades highly suffer from a smoothing effect. The third is related to the border effect of the continuous variable across the boundary of geological domains. The latter means that the final block model of the grade shows a very abrupt transition when crossing the border of two adjacent geological domains. This characteristic of the border effect may not be always true, and it is plausible that some of the variables show smooth or soft boundaries. The case is even more complicated when there is a mixture of hard and soft boundaries. A solution is provided in this paper to employ a cokriging paradigm for jointly modeling grade and geological domains. The results of modeling the copper in an Iranian copper porphyry deposit through the proposed approach illustrates that the method is not only capable of handling the mixture of hard and soft boundaries, but it also produces models that are less influenced by the smoothing effect. These results are compared to an independent kriging, where each variable is modeled separately, irrespective of the influence of geological domains.
Highlights
Mineral resource estimation is the first stage in the exploration and development of a mining project [1,2,3], and its reliability in the downstream of mining activities such as long- and short-term mine planning is inevitable [4,5]
Boundary is soft if the grade shows gradual changes once crossing the adjacent geological domains, and is hard if the changes across the geological boundary are abrupt. Another issue in this hierarchical technique of resource estimation is yielding hard boundaries in the continuous variable when crossing the border of geological domains
This means that this cascade workflow neglects the importance of the border effect if there is a soft boundary in the contact of two adjacent domains [18,19]
Summary
Mineral resource estimation is the first stage in the exploration and development of a mining project [1,2,3], and its reliability in the downstream of mining activities such as long- and short-term mine planning is inevitable [4,5]. Another issue in this hierarchical technique of resource estimation is yielding hard boundaries in the continuous variable when crossing the border of geological domains This means that this cascade workflow neglects the importance of the border effect if there is a soft boundary in the contact of two adjacent domains [18,19]. This approach is suitable for hard boundaries, but it is effective, with less precision, for the soft boundary This method is presented for the case where domains are identified through partitioning the grade (i.e., grade domains), but can still be used for situations where estimation domains are characterized by geological information. The method diminishes the magnitude of the disconnections in the domain boundaries, it does not eliminate them entirely [24]
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