Blocking in Placers

The tested and probable mineral which is estimated in the placing is related to the drillings and fronts of banks which have been sampled and which present laws of economic minerals.

The drilling of exploratory holes is generally performed in nets (the holes are located in the vertices of the quadrilaterals) which are adequate to the characteristics of the mineral deposit and to the accumulated experience on a determined type of mineral deposit. Generally, the mineral deposits which present more regularity in the mineralization require the spacing to be wider than the deposits which present erratic distributions.

The knowledge of the geomorphology and the depositational station regiment allow outlining the primary nets of prospecting and exploration and the encircling of anomalies facilitates the design of secondary nets of drilling to obtain a better precision in the blocking of the mineral.

When the variability of the mineralization is unchanging (isotropic) or one does not know its behavior, one uses squared nets; but if you observe that one direction presents more variability in the mineralization (anisotropic) the intervals of drilling will be less and a rectangular or rhombus net will be adopted.

The exploration for analogy with other similar mineral deposits, especially in placing, makes us use the parameters which have already been used previously. In the case of alluvial deposits, the variability of the values in the concentrations of Au, platinum, diamonds, oxides of tin, wolfranite, among others, is generally between 40% and 200%. Regarding this strong variability, the drilling nets of wells must follow the intervals recommended for irregular and very irregular mineralization.

The blocking will be performed between the holes which are grouped within the anomalies. The blocks of mineral reserves will be defined by the net of exploration or the secondary net.

The cubication will be effectuated following whichever of the following methods: by transversal sections, by polygonal and by triangles. The triangle method is recommended, applying interpellations of the cut-off values for the encircling of the mineral to be exploited.

The calculus of potency and average laws for each triangle will follow the method of the heavy average arithmetic. The calculus of the total reserves will be done in function of the average laws and of the areas of the triangles.

The probable mineral will be located in the periphery of the polygonous formed by the holes with laws of exploitable mineral. The probable mineral will extend to the Interpol led value which is equal to the cut-off or until an equal distance to the ratio of influence, in other words, to the half of the interval the measured between the holes of drilling.