Asadi, Hooshang
d) The N-S magnetic anomaly, which has been modelled on line 255L, coincides with an inferred N-S structure
identified from the geochemical data (Figures 2 and 4). This feature may represent an important, previously
unmapped, fault forming the western boundary of the Iman-Khan unit in this area. From the results of the
quantitative geophysical modelling it is inferred to dip E at about 60 degrees.
e) Results for several drillholes were compared
with the corresponding geochemical results
obtained in soils (Figure 5). This comparison
highlights the considerable enrichment of gold in
soils compared with corresponding grades in 400 200 300 400
drillcore. The soil anomaly shown here Section 10
correlates well with the mapped contact between
the Zarshuran limestones and the granitoid. This 2600 2500
profile then shows a 200m section with soil
values in excess of 1000ppb gold, whereas in the
drillhole which cuts the same units there are only
4 samples with grades greater than 1000ppb, ze gue
representing a single 3m intersection. In
addition the soil geochemistry results suggest the
presence of significant mineralisation within the E our un
Chaldagh limestones, which is not confirmed in Qaradash
the drillhole. This is interpreted as "smearing" sa aire |
of the anomaly over units which were previously ise
overlain by mineralised material, with gold I ze cu cs
having been concentrated in soils after erosion of
their host rocks. This would account for the Figure5. Interpreted geology on drillhole cross-section
scarp-like topography of the main geochemical number 10 (see Figure 4 for location), showing
anomaly shown in Figure 4 (ie sharp gradient on downhole histogram of gold values in drillhole
the SW flank compared with a gently sloping 4 for comparison with profile showing gold
plateau to the NE). Comparison of the results of values in soils (both profiles are log scaled
geophysical modelling with drillhole data was starting at 1ppb gold)
not possible since all the available drillholes are
situated to the south of the main magnetic anomaly.
f) Calculated areas, and average values of gold in soils, for the main geochemical anomalies (Figure 4), were used to
predict the potential volume and grade of the in-situ resource. In this case the inferred in-situ grades were
determined using the log-probability graphs presented in Figure 3. These results are summarised in Table 2.
Anomaly | Area Soils Au | Soils Au Rock Au Vol 100m | Vol 200m | Mass. 100m | Mass 200m
m? In ppb ppb Ppb Mm? Mm? Mt Mt
A 53125 6.26 523 90 0.53 1.06 1.33 2.66
B1 24375 7.12 1236 250 0.24 0.49 0.61 1.22
B2 6250 7.98 2922 500 0.06 0.13 0.16 0.31
B3 32500 7.88 2644 400 0.33 0.65 0.81 1.63
C 94375 6.87 963 175 0.94 1.89 2.36 4.72
TOTAL | 210625 6.93 1201 207 2.11 4.21 5.27 10.53
Table 2. Resource potential inferred from geochemical anomalies for gold in soils. Anomaly areas (column 2) are
used to infer volume and mass to 100m and 200m depth (columns 6-9). The average grade of the soil
anomalies (columns 3-4) are used to infer in situ grade (column 5) using the sample populations identified
on the cumulative frequency plots (Figure 3).
5 CONCLUSIONS
The results presented here indicate that the Zarshuran deposit occurs in an area with exceptionally anomalous values of
gold in soils and very high intensity magnetic anomalies. Careful analysis and modelling of these features in a 2D GIS
88
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000.
