Introduction
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
Types
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.
Mining Reserves
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.
Summary
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.