The 3D geoscience computer modeling and excavation design capabilities of Lynx Geosystems Inc. (Vancouver, Canada) have recently been applied to evaluation and mine planning for an underground copper / zinc deposit in northern Turkey. The deposit includes both structural and mineralogical complexity, and its characterization in terms of grades and tonnages requires a high degree of geological control. Mine planning includes a feasibility study of several alternative underground mine layouts.
Geology of the Deposit
The deposit is a severely faulted, volcanogenic massive sulphide dipping at 75 degrees. Both footwall and hanging wall include interbedded ash and tuff layers that present excavation stability problems, however the hanging wall is capped with a more competent basalt layer. The complexity of the deposit is compounded by the presence of a number of basalt intrusions, or dikes. Surface and underground exploratory drilling of the deposit has been conducted on vertical sections at 40m centers. Topography and fault surfaces are modeled first as triangulated (TIN) surface representations. The latter include three, approximately vertical, transverse faults, and a strike fault that parallels the deposit with an opposing dip of 70 degrees. The second step involves a volume model representation of the intrusive basalt dikes and the basalt capping layer. Within these spatial controls a volume model representation of the extent of the deposit is then interpreted from borehole observations of the distinctive footwall and hanging wall contacts.
Interpretation of Mineralogical Ore
The mineralogy of the deposit includes four ore types, with significant grade variations, that require different milling, concentrating and smelting treatments. For both grade prediction and mine planning purposes the ore type volumes must be represented independently. Within the predefined limits of the deposit, the extent of each ore type is first interpreted on plan sections at 20m vertical spacing and then extended and correlated between sections. The source information for this exercise is provided by mineralogical observations included in the borehole logs. The final result is a detailed 3D volume model representation of the extent of each ore type within the deposit.
Prediction of Mineral Grades
Zinc and copper grades are predicted for a 3D grid data structure using an inverse distance squared interpolation technique. Grade prediction for each ore type is spatially controlled by its volumetric extent, as defined by the ore type model, and based on samples from the ore type. The result is a predicted spatial variation for each mineral that takes full account of the controlling mineralogical characteristic and its spatial discontinuity. To provide an appropriate reference for excavation design purposes, the predicted copper and zinc grades are combined into a single net smelter return (NSR) variable by applying 3D grid manipulation algorithms. An isosurface for the economic grade cutoff through this variation defines the extent of economically mineable ore.
Ore Excavation Design
Mining methods are dictated by the poor rock conditions in the footwall and hanging wall. The final design includes a combination of sublevel retreat and drift and fill stoping. Stoping limits, adits, cross-cuts and access ramps are designed from plan sections using the LYNX interactive design tools. The result is a precise volume model representation of excavation geometry.
Mine Development Design
Several long term options for mine egress development are considered. The primary design consideration is to accommodate as much mine development as possible in the competent hanging wall basalts. Interactive design is performed with reference to the interpretation of basalt layers performed earlier.
Stoping volumes and stoping subunit (drift) volumes are determined in terms of ore types, tonnages and mineral grades. This involves a precise volumetric intersection of excavation volumes, mineral grade variations, and geological/mineralogical volume interpretations (Figure 2). Similar intersections are performed for the mine development volumes, some of which are located within the deposit. The volumetric intersection results also identify sections of mine development that require rock support. These results collectively provide a basis for precise mine planning and estimation of the revenue generating capacity of the mine.
This work was performed by mine and mining contractor personnel, with Lynx personnel involved in a site support consulting role. Completion of the deposit evaluation and feasibility study in a three week period provides a measure of the efficiencies that can be achieved with an integrated computerized approach.