Abstract
This is the first attempt to provide a general mineralogical and geochemical survey of natural Ca2SiO4-bearing combustion metamorphic (CM) rocks produced by annealing and decarbonation of bioproductive Maastrichtian oil shales in the Hatrurim Basin (Negev Desert, Israel). We present a synthesis of data collected for fifteen years on thirty nine minerals existing as fairly large grains suitable for analytical examination. The Hatrurim Ca2SiO4-bearing CM rocks, which are natural analogs of industrial cement clinker, have been studied comprehensively, with a focus on several key issues: major- and trace-element compositions of the rocks and their sedimentary precursors; mineral chemistry of rock-forming phases; accessory mineralogy; incorporation of heavy metals and other trace elements into different phases of clinker-like natural assemblages; role of trace elements in stabilization/destabilization of Ca2SiO4 polymorphic modifications; mineralogical diversity of Ca2SiO4-bearing CM rocks and trace element partitioning during high-temperature–low-pressure anhydrous sintering. The reported results have implications for mineral formation and element partitioning during high-temperature–low-pressure combustion metamorphism of trace element-loaded bituminous marine chalky sediments (“oil shales”) as well as for the joint effect of multiple elements on the properties and hydration behavior of crystalline phases in industrial cement clinkers.
Highlights
High-temperature calcic combustion metamorphic (CM) rocks, ubiquitous in the Hatrurim Formation in Israel (Judean and Negev Deserts) and Jordan (Transjordanian Plateau), are strikingly similar in mineralogy to industrial cement clinkers with high trace-element (Zn, Cd, U, Ni, Cr) content [1,2,3,4,5,6,7,8]
The formation of phases and element partitioning in natural high-temperature–low-pressure metacarbonate CM rocks akin to clinkers are studied in the 4 Ma to 100 Kyr geological structures of the Hatrurim Basin (Table 1) used as test sites, with the natural analog approach successfully tested in the Mottled Zone [5,9,10,11,12,13,14]
All selected samples were analyzed by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and electron probe microanalyses (EPMA), methods at the Analytical Center for multi-elemental and isotope research SB RAS, Sobolev Institute of Geology and mineralogy (IGM), Novosibirsk, Russia
Summary
High-temperature calcic combustion metamorphic (CM) rocks, ubiquitous in the Hatrurim Formation (so-called Mottled Zone) in Israel (Judean and Negev Deserts) and Jordan (Transjordanian Plateau), are strikingly similar in mineralogy to industrial cement clinkers with high trace-element (Zn, Cd, U, Ni, Cr) content [1,2,3,4,5,6,7,8]. Heavy metals are incorporated in cement clinker during the cement kiln co-processing of hazardous wastes either by formation of accessory phases (PbSO4; (Mg,Zn,Ni,Cu)O; Cr- and Ni-bearing spinels and others) or by cation substitutions into the structure of main clinker-forming minerals (Cd2+ → Ca2+; Ni2+ → Mg2+; Ni2+ → Ca2+; Ni2+ → Fe2+; Cr3+ → Al3+; Zn2+ → Al3+). We are trying to bridge the knowledge gaps with this study, which is the first attempt to provide a geochemical survey of natural Ca2SiO4-bearing CM rocks produced by annealing and decarbonation of oil shales in the Hatrurim Basin It encompasses analytical data we collected for fifteen years on thirty-nine minerals (Table 2) existing as fairly large (10–50 μm) well crystallized grains suitable for measuring the contents of their major and trace elements.
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