Reimar Seltmann
Michael L. Zientek
Boris Syusyura
Robert A. Creaser
Alla Dolgopolova
Stephen E. Box
2012
<div class="t m0 x11 h8 y36 ff1 fs5 fc0 sc0 lsb ws37">Sandstone-hosted copper (sandstone Cu) deposits occur within a 200-km reach of the northern Chu-Sarysu basin of central Kazakhstan (Dzhezkazgan and Zhaman-Aibat deposits, and the Zhilandy group of deposits). The deposits consist of Cu sulfide minerals as intergranular cement and grain replacement in 10 ore-bearing members of sandstone and conglomerate within a 600- to 1,000-m thick Pennsylvanian fluvial red-bed sequence. Copper metal content of the deposits ranges from 22 million metric tons (Mt, Dzehzkazgan) to 0.13Mt (Karashoshak in the Zhilandy group), with average grades of 0.85 to 1.7% Cu and significant values for silver (Ag) and rhenium (Re). Broader zones of iron reduction (bleaching) of sandstones and conglomerates of the red-bed sequence extend over 10 km beyond each of the deposits along E-NE-trending anticlines, which began to form in the Pennsylvanian. The bleached zones and organic residues within them are remnants of ormer petroleum fluid accumulations trapped by these anticlines. Deposit sites along these F<span class="fs4 ls3 v3">1</span><span class="lse ws41 v0">anticlines are localized </span>at and adjacent to the intersections of nearly orthogonal N-NW-trending F<span class="fs4 ls4 v3">2</span><span class="v0">synclines. These structural lows </span>served to guide the flow of dense ore brines across the petroleum-bearing anticlines, resulting in ore sulfide precipitation where the two fluids mixed. The ore brine was sourced either from the overlying Early Permian lacustrine evaporitic basin, whose depocenter occurs between the major deposits, or from underlying Upper Devonian marine evaporites. Sulfur isotopes indicate biologic reduction of sulfate but do not resolve whether the sulfate was contributed from the brine or from the petroleum fluids. New Re-Os age dates of Cu sulfides from the Dzhezkazgan deposit indicate that mineralization took place between 299 to 309 Ma near the Pennsylvanian-Permian age boundary. At the Dzhezkazgan and some Zhilandy deposits, F<span class="fs4 ls5 v3">2</span><span class="v0">fold deformation con</span>tinued after ore deposition. Copper orebodies in Lower Permian shale near the Zhaman-Aibat deposit indicate that at least some of the mineralization there is younger than at Dzhezkazgan, consistent with the Re-Os age and with differences in their ore Pb isotopes.</div>
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Society of Economic Geologists
Dzhezkazgan and associated sandstone copper deposits of the Chu-Sarysu basin, Central Kazakhstan
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