Page 93 - Introduction to Mineral Exploration

76 C.J. MOON & M.K.G. WHATELEY

TABLE 5.2 Example of the use of
Assay Zn% Average grade Grade using a 1.5% a grade cut-off to establish the
width at a 1.5% weighted average mining width of a Pb-Zn vein
cut-off cut-off deposit.
0.30 0.01
0.30 0.05
0.30 0.13
0.20 0.17
0.20 0.25
0.20 0.64
0.20 0.92
0.20 1.10
0.20 2.30
0.20 1.20
0.20 2.10 2.26% 1.59%
0.20 5.30 over over
0.23 1.40 2.10 m 3.40 m
0.15 2.00
0.20 1.90
0.20 1.80
0.20 1.30
0.20 2.60
0.12 3.50
4.00 m 1.35% (overall average)

weighting function. The weighted average is (Box 5.2). In coal analytical work there are
calculated until the average falls above the cut- several ways in which the proximate analyses
off, which in this case makes 1.59% Zn over (moisture, volatile, ash, and fixed carbon con-
3.40 m. The inclusion of just one more sample tents) can be reported; e.g. on an as received,
would bring the average down below 1.5%. The moisture free or dry, ash free basis (Stach 1982,
overall weighted average is 1.35% Zn over Speight 1983, Ward 1984, Thomas 1992).
4.00 m. A similar form may well be utilized for sand
and gravel or crushed rock analyses where the
geologist requires special test work on his or
5.1.5 Laboratory program
her samples, such as size analysis, aggregate
Once the samples have been collected, bagged, crushing value (ACV), or polished stone value
and labeled, they must be sent to the laboratory (PSV) to name but a few.
for analysis. Not only must the elements of In today’s computerized era, results are often
interest be specified, but the type of analyt- returned to the company either on a floppy disk
ical procedure should be discussed with the or direct to the company’s computer from the
laboratory. Cost should not be the overriding laboratory’s computer via a modem and a tele-
factor when choosing a laboratory. Accuracy, phone link. Care must be taken when entering
precision, and an efficient procedure are also the results thus obtained into the company’s
needed. An efficient procedure within one’s database, that the columns of data in the labor-
own office is also required. Sample numbers atory’s results correspond with the columns
and the analyses requested should be noted in your own data base (discussed in detail in
down rigorously on a sample control form section 9.1). Gold values of several percent and
(Box 5.1). copper values in the ppb range should alert
An alternative practice is to state clearly the even the most unsuspecting operator to an
instructions for test work on the sample sheet error!