Tuff Soil 3e5n68

Deposit Description The Sarbay skarn iron deposit is located within north-eastern Kazakhstan, near K ustanay, to the south-east of Magnitogorsk. The deposit lies near the western of the Sarbay diorite which comprises pyroxene and quartz diorite and diorite porphyry, accompanied by a series of dyk es, which include pre-ore diorite porphyry and post ore quartz-pyroxene porphyri es and granite porphyries. Within the district, the intruded sequence is compose d of the interstratified lower Carboniferous andesite porphyries and their tuffs , tuff-breccias, tuffaceous sediments, limestone, sandstone and tuffaceous sands tone, overlain by middle and upper Carboniferous hematised tuffs, as well as lav as and tuffs of basaltic composition, tuffaceous sediments and argillites. The r ocks of this sequence are developed into the near north-south Sokolovsk-Sarbay a nticline, with the Sarbay deposits being developed on its western limb (Smirnov, 1977). In the vicinity of the ore deposits there is extensive pre-, intra- and post-ore fracturing developed, with diorite porphyries having been injected along near n orth-south pre-ore faults, dipping at 65 to 70°W. The intra-ore fracturing is defi ned by the vein-like skarn-magnetite partings which cut the bedding. A system of post-ore faults has produced a block faulting pattern and crushing of the ore a nd skarns, and in places controls the distribution of post-ore quartz-diorite po rphyries and granite-porphyry dykes (Smirnov, 1977). Alteration comprises the following stages: i). pre-ore hornfelsing, mainly within the tuffs and tuffaceous sediments, decre asing in intensity away from intrusive s; ii). the formation of biotite-K feldspar and albite alteration; iii). the development of ore stage skarns, comprising pyroxene-scapolite, pyroxe ne-garnet, scapolite-pyroxene-garnet and epidote-actinolite. The scapolite alter ation is only developed after feldspar rocks, although the skarns and calc-silic ates are formed after all preceding rocks, including hornfels and earlier altera tion products; iv). post-ore propylitic suites of chlorite-prehnite, calcite-quartz and zeolite which accompany zones of late tectonic disturbance. Chlorine bearing sodic scap olite is a widespread alteration product, implying NaCl metasomatism (Smirnov, 1 977). At the Eastern and South-eastern orebodies there is a zonation outwards from the intrusive as follows: i). biotite-albite-scapolite over a width of 100-150 m; ii). garnet and garnet-pyroxene skarn forming a 3 to 20 m thick zone in the foo twall of the Eastern and South-eastern orebodies; iii). ore stage and skarn hosted ore with scapolite, 50 to 185 m thick; iv). skarn and scapolite-pyroxene alteration from 3 to 20 m thick in the hanging wall to ore; v). pyroxene skarns with relicts of hornfels, 10 to 30 m thick; vi). pyroxene-plagioclase hornfels, partly scapolitised and skarn altered, up to 40 m thick; vii). hornfelsed and albitised tuffs and tuffaceous sediments up to 160 m thick (Smirnov, 1977). In contrast, the Western orebody is within an alteration pattern, of albitised, prehnitised and zeolite altered tuffs and tuffaceous sediments, replaced by acti nolite and chlorite altered pyroclastics, followed by ores and mineralised epido te-actinolite, un-mineralised epidote-actinolite, and finally a zone of variably developed epidote, actinolite, prehnite and zeolite alteration (Smirnov, 1977). The orebodies at Sarbay consist of layer like, conformable masses. They are conf

ined to a 350 to 400 m thick interval of the Visean (mid-lower Carboniferous) li mestone-tuff-tuffaceous sediments sequence of the Valerianovsk Group. The host i nterval originally comprised dark-grey bituminous limestone, interstratified wit h calcareous tuffs and tuffaceous sediments. The orebodies have the shape of elo ngated lenses of quite well defined thickness, prior to lensing out along strike . The Eastern orebody has a length of 1700 m and thickness of 185 m, and has bee n traced down dip for more than 1000 m; the South-eastern orebody has a strike o f 1000 m, thickness of 170 m and down-dip extent of >800 m; while the Western or ebody has respective dimensions of 1400 m, 185 m and 1700 to 1800 m in its centr al section (Smirnov, 1977). The orebodies at Sarbay do not come into with the diorite-porphyry intru sion, being separated by 25 to 150 m of barren skarns and alteration. Ore format ion appears to be connected with pre-ore fault channels, rather than the intrusi ve . The ore comprises alternating layers of uniform ores, ore bearing sk arns and non-ore skarns. The orebody is around 50% uniform-massive ore with >50% Fe, and half skarn ore with 20 to 50% Fe. Around 1% of the ore is oxidised. Mag netite is the primary ore mineral with subordinate associated pyrite, pyrrhotite -pyrite and lesser magnetite, chalcopyrite and sphalerite occurring as layers in the footwall of the magnetite ore lenses (Smirnov, 1977). The uniform-massive magnetite has a banded texture, inherited from the primary c alcareous tuffs and limestones. In addition to the dominant magnetite the ore co ntains pyroxene, scapolite, garnet, wollastonite, albite, epidote, actinolite, a patite, pyrite, calcite, quartz, and accessory idocrase and sphene. Rare pyrrhot ite, arsenopyrite, sphalerite, galena and chalcocite are also recorded. The lowe r grade skarn-ores are also coarsely banded, mimicking the original banding of t he sediments and tuffs. Mineralised assemblages include pyroxene-magnetite and g arnet-magnetite skarns; scapolite-skarn consisting of scapolite-pyroxene-garnetmagnetite; hydrosilicates of epidote-actinolite-magnetite. The skarn and scapoli te-skarn associations include some syn-skarn wollastonite and apatite, as well a s post-skarn albite, epidote, actinolite, chlorite, sulphides, calcite, quartz a nd zeolite (Smirnov, 1977). The ore contains 15 to 19% SiO2, 0.25 to 0.36% Al2O3, 5.3 to 11.1% CaO, 0.25 to 0.36% TiO2, 0.02 to 0.1% V2O5, 0.1 to 0.2% MnO, 0.03 to 0.05% Cu, 0.03 to 0.08% Zn, 0.015 to 0.02% Pb. The higher grade reserves, with >30% Fe, as quoted in 1977, amounted to 725 Mt o f ore @ 45.6% Fe, 4.05% S, 0.13% P. The deposit was being mined from an open cut , with a potential resource of 1500 Mt at depth (Smirnov, 1977). The most recent source geological information used to prepare this summary was d ated: 1977. This description is a summary from published sources, the chief of which are lis ted below. © Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, s torage or dissemination prohibited.