Dolerites solidified in a salt formation

Abstract

During the Late Paleozoic or Early Mesozoic the Zayarskaya dolerites (diabases) were intruded into rocks of the Lower Cambrian Usol'ye series (salt strata separated by carbonate and sulfate-carbonate layers) in the Angara-Ilim watershed area of the Irkutsk amphitheater. Both field observations of the two dolerites intruded into salt strata and experimental data on the system dolerite-NaC1 indicate these dolerites were implaced at low water-vapor pressures. They appear little changed except for veinlets or inclusions of halite and calcite, and rocks of skarn mineralogy result where they have intruded nonsalt strata. Contacts between dolerites and salt are sharp, and between the NaCl and dolerite melts none of intermediate composition were found experimentally. In general, iron-bearing sublimates are evolved from the superposition of trap magma onto halogen rocks. No migration of volatile iron chlorides is evident in the Zayarskaya intrusives because the requisite high water-vapor pressures and outlet channels (fissure system, fractures, etc.) were absent. --P. W. Wood. * * *The possible participation and role of halogens in the endogenous processes, chiefly in mineralization, have long been of interest to geologists. Of course, any consideration of this problem requires information on the behavior of halogens under the conditions of high temperatures and pressures prevailing in a particular geological situation. This article deals with two dolerite intrusions solidified in salts that had been uncovered by a Zayarskaya borehole, as well as with the findings of experimental research into the fusion of artificial mixtures of dolerites and rock salt.The Zayarskaya borehole was drilled during 1957 -1958, in the middle of the Irkutsk amphitheater between the him river and its upper course and the Angara river. At present this region is inundated by the waters of the Bratsk dam; the borehole core was transported to Irkutsk, where it was analyzed by the present writers. Our observations of the core were of a fairly fragmentary nature, owing not only to the poor condition of the core and its markings but also to the fact that from the very beginning only a minimum number of samples was collected during the drilling of dolerites and, moreover, these samples had been used by oilmen. It was possible to partially fill this gap by investigating a number of samples provided by Z.N. Ipatova (VNIGRI) [All-Union Petroleum Scientific Research Institute of Geological Exploration], and the authors take this opportunity to express to her their gratitude. In the following description of the geological situation and cross section of the discovered deposits we repeatedly utilized the findings of a published report by Z. A. Kondrat'yeva and Z.N. Ipatova (3). Translated from Dolerity, zastyvshiye v solyanoy tolshche, Izv. AN SSSR, ser. geol., 1968, no. 2, P. 52-63. The authors are with the Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, AN SSSR <IGEM), Moscow.The Irkutsk amphitheater on the whole represents a...

Metasomatism and ore formation at contacts of dolerite with saliferous rocks in the sedimentary cover of the southern Siberian platform

“…(1) Volcanomictic rocks of crater lakes, the Lower Triassic Neryunda Formation ( T 1 nr ); (2) explosion breccia, lava flows, and pyroclastic rocks, the Lower Triassic Korvunchan Formation (T 1 kr); (3) Lower Carboniferous-Permian poorly lithified coal-bearing sequence (C 1 -P); (4) red mudstone, siltstone, and marlstone with sporadic sandstone interlayers, the Lower Silurian Yarsk Formation (S 1 jr); (5) sandstone with carbonate-clayey interlayers, the Lower Silurian Kezhem Formation (S 1 kz); (6) red mudstone and marlstone with sporadic sandstone interlayers, the Middle-Upper Ordovician Bratsk Formation (O 2-3 br); (7) quartz sandstone, the Middle Ordovician Mamyr Formation (O 2 mm); (8) limestone, the Lower Ordovician Ust-Kut Formation (O 1 uk); (9) marlstone with interlayers of fine-grained calcareous sandstone, siltstone, gypsum, and limestone, the Middle-Upper Cambrian Verkholensk Formation ( vl); (10) dolomite of the Lower-Middle Cambrian Litvintsevo Formation ( lt); (11) dolomite and rock salt with mudstone and siltstone interlayers, the Lower Cambrian Angara Formation ( an); (12) massive dolomite, the Lower Cambrian Bulai Formation ( bl); (13) dolomite and anhydrite with salt interlayers, the Lower Cambrian Bel'sk Formation ( bls); (14) sandstone, siltstone, and mudstone at the bottom of the platform cover, the Riphean-Vendian Ushakovo Formation (R-Vush), and Precambrian crystalline schists of the basement (p ); (15) intrusive bodies of the trap complex: sills, laccoliths, dikes, and offsets of dolerite bodies; (16) skarnified dolerite in the zone of mingling of dolerites and evaporites; (17) magnesian and calcic skarn, skarnoid, and calciphyre; (18)(19)(20)(21)(22)(23)(24) iron orebodies: (18) conformable orebodies in magnesian skarn and calciphyre, (19) halite-magnetite ore in the Angara Formation, (20) ore stockwork in the Verkholensk Formation, (21) bedding plane calcite-magnetite ore in limestone of the Ust-Kut and Kezhem formations, (22) telescoping orebodies in diatremes, (23) near-vertical banded, oolitic, and brecciated ore hosted in volcanic and pyroclastic rocks, (24) ore veins localized beneath sills and fill of late fissures; (25) faults; (26) bottom of the platform cover remaining unexplored with respect to iron ore formation. variable saturation with fluids, and contrasting composition, the magmatic melts form branching bodies of complex morphology.…”