پديد آورندگان :
قاسملو, آيسان دانشگاه زنجان - گروه زمين شناسي , كوهستاني, حسين دانشگاه زنجان - گروه زمين شناسي , مختاري, مير علي اصغر دانشگاه زنجان - گروه زمين شناسي , زهدي, افشين دانشگاه زنجان - گروه زمين شناسي
چكيده لاتين :
Sediment-hosted stratabound copper (SSC) deposits can be defined as stratabound deposits,
consisting of
disseminated to veinlet native copper and copper sulfides hosted by chemically reducing
sedimentary rocks, including organic-rich black shales (Cox et al., 2007; Hitzman et al., 2005;
Hayes et al., 2015). SSC deposits occur in three subtypes divided by host lithology and by the
corresponding type of reductant that precipitated sulfur and Cu from warm, oxidized,
metals-transporting, sedimentary brines: (1) reduced-facies type (e.g. Kupferschiefer and
Zambia deposits), (2) sandstone-type (Revett) (e.g., Spar Lake, hosted in the Revett
Formation in Montana, USA), and (3) Redbed type (e.g. Nacimiento in New Mexico and Paradox basin’s
deposits in Colorado and Utah).
SSC deposits in Iran are usually formed during late Triassic, late Jurassic-early Cretaceous, and
Miocene. They are mostly discovered in the Garadou Red Formation of the Ravar-Tabas basin and the
Upper Red Formation (URF) in the Avaj-Zanjan-Tabriz-Khoy (AZTK) area. SSC deposits in the
AZTK area, northwestern Iran, hosted by grey sandstone units of the URF. The Tasouj,
Tazekand, Nahand-Ivand, Ortasou, Chehrabad, Hamzelou, Halab, Zaghelou and Avaj are the main
important deposits in the AZTK area. These deposits consist predominantly of bedding-parallel
replacement and disseminated Cu (Pb–Zn) sulfides, roughly concordant with the stratification.
Excepting small scale geological maps of the area, i.e., 1:250,000 geological maps of
Takab and 1:100,000 geological maps of Mahneshan and a number of unpublished Cu exploration
report, prior to this research no work had be done on Cu mineralization at Hamzelou.
The present paper provides an overview of the geological framework, and the
mineralization characteristics of the Hamzelou deposit with an application to the ore genesis.
Identification of these characteristics can be used as an exploration model for this type of Cu
mineralization in this area and elsewhere.
2-Materials and methods
Detailed field work has been carried out at different scales in the Hamzelou area. During the field
works, detailed stratigraphic sections were measured, sampled and described. Additionally,
color of the sandstone layers and the presence of plant fossils were scanned during the field
work. About 29 polished thin and thin sections from host rocks and mineralized layers were studied
by conventional petrographic and mineralogical methods at the University of Zanjan. In addition, 8
samples from barren red and grey host sandstones and mineralized samples were analyzed by ICP-MS
for trace elements and REE at Zarazma Co.,
Tehran, Iran.
The Hamzelou Cu deposit, 70 km northwest of Zanjan, is located in the Central Iranian zone. Rock units
exposed in this area belongs to the URF, and consist of alternations of red and green marl intercalated
with red to grey, medium- to thick-bedded sandstone. In this area, URF has 945 m thickness and consist of four main parts. These parts, from bottom to top, consist of 1- alternation of evaporates and
gypsiferous green marls (300 m), 2- alternation of red marl and grey to red sandstone (355 m), 3-
alternation of red and green marl intercalated with grey to red sandstone (150 m), and 4- altenation of
green marls and green siltstones (140 m).
Cu mineralization in the Hamzelou deposit occurred in grey microconglomerate and sandstone units of
the second part of the URF. Mineralization often formed around and within the fragments of the plant
fossils, in the form of disseminated and solution seems sulfides. Based on field studies, mineralization at
Hamzelou deposit occurred in two distinct northern and southern parts of reduced-grey
microconglomerate and sandstone layers, with about 1.5 and 2 m thickness and about 200 and 1000 m
length, respectively. The ore horizons contain red oxidized zone, bleached zone and mineralized reduced
zone which the latter is located within the bleached zone. The red oxidized zone consists of red marl and
sandstone layers containing of iron oxides which is located adjacent to the reduced horizons. The red
color of this zone caused by the presence of iron oxides around the grains. The oxidized pyrite crystals are
the main important minerals in this zone. Bleached zone is part of sandstone and microconglomerate
sequences that the alteration processes caused changing in its color. Grey and green colors in this zone
occurred by the presence of organic materials and diagenetic pyrites. Mineralization in reduced zone has
occurred within the organic materials-bearing bleached zones. Plant debris, plant fossils, diagenetic
pyrites and permeability of host rock had main important role for the Cu mineralization at Hamzelou
deposit.
Chalcocite, and pyrite are the main ore minerals at Hamzelou deposit. Malachite, azurite, covellite,
atacamite, goethite and hematite are formed during supergene processes. Disseminated and cemented
textures along with lens-shaped, solution seems, replacement, and framboidal pyrite are the main ore
textures at Hamzelou deposit.
Comparison of Chondrite normalized trace elements and REE patterns of barren red and grey host sandstones
and mineralized samples at Hamzelou indicate that mineralized samples show lower concentrations of trace
elements and REE relative to host rocks. This signature indicates mobility of these elements during bleaching
and mineralization processes.
Based on tectonic setting, host rock, geometry, presence of plant fossils, ore structure and texture and
mineralogy, it can be concluded that the Hamzelou deposit is a sediment-hosted Redbed type Cu deposit.
