Page 255 - Introduction to Mineral Exploration

238 M.K.G. WHATELEY & B. SCOTT

1.22 1.11 1.16 1.08 1.03 1.00

1.08 1.19 1.12 1.03 1.01

1.08 1.05 1.03 0.97 1.00 0.92 0.94

1.05 1.03 0.97 1.03 1.00 0.95
0 100 m

FIG. 10.20 A portion of a borehole grid illustrating some of the pairs 300 m apart in an E–W direction. (From
Whateley 1992.)

γ γ (h) γ (h)
γ
0.012
Range (a)
0.010
Sill (C + C o )
0.008

0.006
C
0.004
0.002
0 h C o
0 100 200 300 400 500 600 h
Distance (m) 0 100 200 300 400 500 600
Distance (m)
FIG. 10.21 A plot of the experimental semi-variogram
constructed from the data derived from the portion FIG. 10.22 The idealized shape of a semi-variogram
of the borehole grid shown in Figs 10.18–10.20. The (spherical model). (From Whateley 1992.)
calculations are shown in the text.

that there is a large degree of variability be- It is important to note that the rate of
tween the samples. When h is greater than or increase in variability with distance may
equal to a then the data show no correlation depend on the direction of a vector separating
and this gives a random semi-variogram. This the samples. In a coal deposit through which a
can be interpreted to mean that sample spacing channel passes, the variability in the coal qual-
is too great. ity and thickness in a direction normal to the