Asadi, Hooshang
weakly mineralized (Figure 1). The main faults present trend northeast-southwest and northwest-southeast in the
Precambrian formation. Gold occurs mainly as disseminations in carbonaceous, siliceous, and calcareous beds within
the Zarshuran black shale. Gold is also found in hydrothermal veins of massive quartz (jasperoid) and quartz veinlets
formed by carbonate replacement along high-angle faults in Chaldagh limestone. The Chaldagh limestone is also
mineralized at its contacts with the Iman Khan schist and with the overlying Zarshuran unit.
630600 630800 631000 631200 631400 691600 631800 632000 692200
T 2 T T T T T TTA
17°00" E ATISE $
4066800 | =
N Zarshuran Deposit
Agh-Darreh
36940" N arshuran i M >
4066600 J 4066600 Bel aps Rumi
Shir-Ma //
4066400 | 066400 Takhte-Soleiman
(/ (ancient place) 54m
eum
4066200 — Road
7 e Village
629 N Fw Takab Town
4066000 _
; :
Alluvium
4065800 |- Oom Formation (conglomerate)
Granitoid
Soltanieh Formation (dolomite)
Oaradash Formation (tuff and shale)
Jasperoid
Limestone
Zarshuran Unit (black shale)
ChaldaghUnit (limestone)
4065600 |-
4065400 F Projection UTM zone 38
OO mes
b meters 500 T : :
405200 L. , i ; 1 : pe Iman-Khan Unit (schist)
690600 690800 691000 691200 691400 691600 691800 692000 692200
ess Fault
Figure 1. Location and detailed geology of the Zarshuran gold deposit, NW Iran.
Quartz, calcite, dolomite and clays are the principal minerals of the host rocks. Decalcification, silicification, and
argillization characterize mineralized rocks. Decalcification increased the porosity and permeability of the host rocks
and thus provided favorable sites for hydrothermal mineralization. The ore consists mainly of orpiment and pyrite, and
to a lesser extent sphalerite, galena, realgar and stibnite, with subordinate cinnabar, HgS, lorandite, TIAsS», christite,
TIHgAsS3, coloradoite, HgTe, getchellite, AsSbS;, aktashite, CucHg;As,S,,, baumhuerite, Pb,As,So, boulangerite,
Pb;Sb,S;;, geochronite, Pb;4(Sb, As)sS»5, plagionite, PbsSb;S,; and twinnite, Pb(Sb, As);S,. Sulfide oxidation is mainly
confined to veins, veinlets, and fracture zones. Quartz, calcite, fluorite, hematite and barite are the main gangue
minerals. Accessory minerals include apatite, Cas(PO4); (OH, F, CI), rutile, TiO», zircon, ZrSiO;, and xenotime, YPO,
(Asadi et al., 2000). Gold is rarely visible but occurs invisibly in arsenian pyrite and sphalerite (Asadi et al, 1999).
The petrography, mineralogy and trace element geochemistry of the Zarshuran gold deposit show that it is
a Carlin-like sediment-hosted disseminated gold deposit. The association of mineralisation at Zarshuran
with a magmatic intrusion, and the presence of tellurium in concentrations sufficient to precipitate
telluride, suggest a greater magmatic component in the mineralising hydrothermal solution than is typical
for most Carlin-type deposits, best known in the western United States (Asadi et al., 1999 and 2000).
3 GIS DATA INPUTS
The geological maps on a district scale (1:10 000) and deposit scale (1:2000), 19 geological cross sections on a deposit
scale (1:2000), a topographic map at a scale of 1: 2000 and bore hole locations were digitized using the Integrated Land
and Water Information System (ILWIS) GIS.
The geochemical data available were derived from samples taken on a surface grid with a 100m by 20m sampling
interval which covered an area of about 9km’ (larger than the area shown in Figure 1). A total of 4500 surface-soil
samples were collected from the grid and were analysed for Au, As, Sb, Ag, TI, Hg, Cu, Pb, and Zn; these elements
having been selected as direct and pathfinders indicators for gold mineralisation in an epithermal setting. The analyses
were performed using atomic absorption spectrophotometry (AAS) at the Karaj Geochemical Laboratory in Tehran,
Iran. The results were obtaned in the form of hardcopy data listings, which included the sample numbers, coordinates
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000. 83
