“THE CASSIAR STORY”

Mine Planning

G. Scott Zimmer, Mine Engineer,
Cassiar Asbestos Corporation Limited,
Cassiar, B.C.

Abstract

Mine planning at Cassiar consists of an annual cycle of
projection, control, evaluation and revision following com-
pletion of annual diamond drilling during the summer
months. The inherent difficulty in evaluating fibre grade and
distribution, combined with a high-wall phase or push-back
mining system, requires continuous modification to designs
and schedules based on a cumulative evaluation of equip-
ment performance and prediction versus production. To
expedite the planning sequence, a mini-computer system
has been introduced which allows emphasis to be placed on
optimizing designs, exempting personnel from manual cal-
culations and tabulations.

Introduction

SINCE 1971, Cassiar has been carrying out an exten-
sive diamond drilling program to further define the
limits of the orebody in terms of tonnage and grade.
Evaluation of drilling data indicated sufficient ore of
suitable quality to warrant an ongoing expansion of
operations and facilities. In order to provide a base for
sound decision making, Cassiar’s mine planning pro-
cedures have undergone a substantial change since
1973 with the review of old procedures and the intro-
duction of a mini-computer.

Mine planning at Cassiar can be summarized as an
annual cycle consisting of ore and waste projection,
control, evaluation and revision. This entails the re-
vision of the ore reserve figures after the evaluation
of the annual drilling program, a sub-division of re-
serves into mining increments, engineering control and
direction of mining operations, a reconciliation and
evaluation of production with initial projections and,
finally, a modification of reserves based on the pro-
duction evaluation in preparation for use in conjunc-
tion with new drilling data to begin the annual cycle
again.

G. Scott Zimmer was born in the
U.S.A. and educated at Michigan
Technological University from 1962
until 1966, majoring in geological en-
gineering. He joined United Keno Hill
Mines Limited in 1967 as senior ex-
ploration geologist. From 1969 until
1970, he was employed as a staff geol-
ogist in the consulting firm of R. G.
Hilker Limited in Whitehorse. In 1970,
he joined Conwest Exploration Com-
pany Limited as a staff geologist,
progressing to resident geologist in charge of the White-
horse office. He joined Cassiar Asbestos Corporation
Limited in 1972 as mine geologist and became mine engi-
neer in 1978. He is a Member of the CIM and a Fellow
of the Geological Association of Canada.

Keywords: Cassiar Mine, Mine planning, Drilling, Samp-
ling, Pit design, Reserve calculations, Scheduling, Com-
puters.

There are three fundamental problems to consider in
medium- to long-range planning. Two of the diffi-
culties are fibre related; the third is due to a mining
method commitment.

The first fibre-related problem is the difficulty of
developing a rapid and consistent method of deter-
mining fibre content to an absolute or standard base.
A new test mill system is currently being installed, but
until the system is operational, all “assay” data used
in mine planning are based on C.C.R.G. (Corrected
Core Reading Grade). The relationship of C.C.R.G.
with R.M.G. (Recoverable Mine Grade) is entirely
dependent on mill efficiencies.

The second fibre-related difficulty is in assigning a
rock value ($/ton) to future ore for evaluation pur-
poses. Cassiar produces different fibre grades with
values ranging from $320 per ton to $3,620 per ton. It
is theoretically possible to produce nearly all of these
products from any ore grade. Accordingly, derivation
of rock value is again a function of mill efficiency and
relies heavily on historical product distribution and
market demands.

The third constraint is a commitment to a push-
back or phase mining concept due to an ever-increasing
hanging-wall depth [currently 1000 ft (304.8 m) ver-
tical and increasing to at least 1600 ft (488 m) over
the mine life], which imposes severe restrictions on
ore availability and flexibility, requiring critical ore
and waste scheduling, as well as constant evaluation
to ensure ore continuity between phases.

Reserve Calculations and Pit Design

Mine planning procedures have been simplified as
much as possible in order to produce a general flow
sheet (Fig. 1). The foundation for planning consists
of a master set of bench plans covering the entire ore-
body at mining bench intervals: 45 ft (13.7 m) in
waste and 30 ft (9.1 m) in ore. These plans carry
lithology, macro-structure, a fibre to no-fibre inter-
polated (to 3.0% C.C.R.G.) contact and high-grade
zones within the “ore” limits. The fibre-bearing zone
on each bench within the 3.0% C.C.R.G. contour is
sub-divided into blocks, nominally 100 ft (30.5 m) by
100 ft (80.5 m), based on drill-hole intersections.
Computer input of block areas, C.C.R.G. grade and
C.C.R.G. length distribution for each bench produces
a master grade-block model for the fibre-bearing zone
which is independent of economic cut-off grade, mining
limits and topography. Details of master model de-
velopment are covered under “‘Computer Applications’.
The up-dated master model provides the base for
economic evaluation and mining projection of the ore-
body.

Prior to establishing pit limits, a costing exercise is
carried out to define the economic cut-off grade (cur-
rently established at 3.0% C.C.R.G.). This exercise
can be complicated due to the probability that much of
the low-grade material below a given cut-off grade
would necessarily be mined as waste due to access
considerations.

Also prior to establishing or revising pit limits,
structural geology must be evaluated to derive an
optimum slope design for various zones of the proposed
pit. It should be noted that one of the advantages of
phase mining is that intermediate phases may be
treated as trial slopes so that design parameters can

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