Using iron formations during exploration for c. 1.9 Ga Zn-Pb-Ag sulphide deposits, Jugansbo area, Bergslagen, Sweden

2020 ◽  
Author(s):  
Nils Jansson ◽  
Rodney Allen
Keyword(s):  
Geological Mapping ◽  
Iron Formation ◽  
Sulphide Mineralization ◽  
Fine Grained ◽  
Stratigraphic Analysis ◽  
Mineralization Processes ◽  
Volcaniclastic Rocks ◽  
Thermochemical Reduction ◽  
Stratigraphic Evolution ◽  
Iron Formations

<p>Oxide- and silicate-dominated, stratiform iron formations are abundant in the northern part of the Sala inlier, Bergslagen, Sweden. The iron formations are commonly laminated and are associated with fine-grained siliciclastic and felsic volcaniclastic rocks in a 1.91-1.89 Ga succession dominated by pumiceous and lithic-bearing rhyolitic volcaniclastic rocks. Depositional features are consistent with a volcanically active, submarine environment, in which the iron formations and fine-grained host strata to sulphide mineralization accumulated during pauses in volcanism. At c. 1.87-1.81 Ga, the succession underwent polyphase folding and shearing under lower amphibolite facies conditions, followed by polyphase faulting under more brittle conditions.</p><p>The iron formations are locally directly stratigraphically overlain by  stratiform Zn-Pb-Ag sulphide mineralization. Detailed geological mapping has demonstrated that sulphide-bearing (proximal) iron formation is gradational into sulphide-poor (distal) iron formation along a strike extent of more than 7 km. Proximal iron formation is dominated by magnetite, grunerite, tremolite, quartz, almandine-rich garnet (Alm<sub>54</sub>Sps<sub>35</sub>Grs<sub>8</sub>), muscovite, and chlorite, whereas distal iron formation is characterized by hematite, magnetite, epidote, actinolite, spessartine-rich garnet (Sps<sub>53</sub>Adr<sub>29</sub>Grs<sub>15</sub>) and locally calcite. </p><p>Elevated contents of Mn, Zn and Co are observed in both distal and proximal iron formation, whereby these elements help pinpoint the favorable horizon, but are of less use for vectoring along strike. Whole-rock lithogeochemistry samples of proximal iron formation differ from distal iron formation in: (1) Eu/Eu*>1, (2) Ce/Ce*<1, (3) suprachondritic Y/Ho, (4) elevated Tl, Cs, Cd, Sn, S, Cu, Pb, Sb and Au (5) lower volcaniclastic/siliciclastic content based on lower Al, Ti and Zr. Collectively, these features are indicative of Fe mineralization following interaction of a hot, acid and reduced hydrothermal fluid with oxidized seawater in a vent proximal position which was deprived of clastic or volcaniclastic input.</p><p>Sulphide mineralization, ranging from banded, to disseminated and fracture-hosted, is associated with chlorite-rich, locally graphitic mudstone immediately overlying proximal iron formation. Multi-grain δ<sup>34</sup>S<sub>V-CDT</sub> of sphalerite, pyrite and pyrrhotite are exclusively negative, ranging from -10.6 to -0.25 with no clear mode. The δ<sup>34</sup>S<sub>V-CDT</sub> distribution is unusual for Bergslagen deposits, and is indicative of a significant contribution of sulphur via bacteriogenic or thermochemical reduction of seawater SO<sub>4</sub><sup>2-</sup>.</p><p>Stratigraphic analysis suggest that proximally, the mineralizing event followed a sudden deepening of the basin, and progressed from Fe oxide to polymetallic sulphide mineralization. The temporal zonation probably reflect a decrease in the redox potential of the basin, possibly due to venting and ponding of reduced hydrothermal fluids. Ore textures and host facies are consistent with of an exhalative mode of formation for both deposit types, albeit an importance of subseafloor mineralization processes is implied by lateral variability in both sulphide and chlorite content. In relation to the local stratigraphic evolution in the area, the mineralizing event can be directly linked to an event of basin deepening following a caldera-forming volcanic eruption. The results from stratigraphic analysis along with aforementioned proxies for redox and vent-proximity present first order vectors to stratiform Zn-Pb-Ag mineralization in the Jugansbo area, Bergslagen.</p>

scholarly journals Stratigraphy and lithogeochemistry of the Goldenville horizon and associated rocks, Baie Verte Peninsula, Newfoundland

2021 ◽  
Author(s):  
C Mueller ◽  
S J Piercey ◽  
M G Babechuk ◽  
D Copeland
Keyword(s):  
Gold Mineralization ◽  
Iron Formation ◽  
Fine Grained ◽  
Hydrothermal Sediment ◽  
Post Archean Australian Shale ◽  
Oxygenated Water ◽  
Volcaniclastic Rocks ◽  
Laurentian Margin ◽  
Mn Oxides ◽  
Hydrothermal Venting

The Goldenville horizon in the Baie Verte Peninsula is an important stratigraphic horizon that hosts primary (Cambrian to Ordovician) exhalative magnetite and pyrite and was a chemical trap for younger (Silurian to Devonian) orogenic gold mineralization. The horizon is overlain by basaltic flows and volcaniclastic rocks, is intercalated with variably coloured argillites and cherts, and underlain by mafic volcaniclastic rocks; the entire stratigraphy is cut by younger fine-grained mafic dykes and coarser gabbro. Lithogeochemical signatures of the Goldenville horizon allow it to be divided into high-Fe iron formation (HIF; >50% Fe2O3), low-Fe iron formation (LIF; 15-50% Fe2O3), and argillite with iron minerals (AIF; <15% Fe2O3). These variably Fe-rich rocks have Fe-Ti-Mn-Al systematics consistent with element derivation from varying mineral contributions from hydrothermal venting and ambient detrital sedimentation. Post-Archean Australian Shale (PAAS)-normalized rare earth element (REE) signatures for the HIF samples have negative Ce anomalies and patterns similar to modern hydrothermal sediment deposited under oxygenated ocean conditions. The PAAS-normalized REE signatures of LIF samples have positive Ce anomalies, similar to hydrothermal sediment deposited under anoxic to sub-oxic conditions. The paradoxical Ce behaviour is potentially explained by the Mn geochemistry of the LIF samples. The LIF have elevated MnO contents (2.0-7.5 weight %), suggesting that Mn from hydrothermal fluids was oxidized in an oxygenated water column during hydrothermal venting, Mn-oxides then scavenged Ce from seawater, and these Mn-oxides were subsequently deposited in the hydrothermal sediment. The Mn-rich LIF samples with positive Ce anomalies are intercalated with HIF with negative Ce anomalies, both regionally and on a metre scale within drill holes. Thus, the LIF positive Ce anomaly signature may record extended and particle-specific scavenging rather than sub-oxic/redox-stratified marine conditions. Collectively, results suggest that the Cambro-Ordovician Taconic seaway along the Laurentian margin may have been completely or near-completely oxygenated at the time of Goldenville horizon deposition.

scholarly journals MAPEAMENTO GEOLÓGICO DA REGIÃO DA SERRA DOS TURVOS, CARATINGA (MG), SETOR SUL DO ORÓGENO ARAÇUAÍ

2012 ◽  
Author(s):  
Gláucia Queiroga ◽  
Tiago Novo ◽  
A. C. Pedrosa-Soares
Keyword(s):  
Sedimentary Cover ◽  
Granulite Facies ◽  
Geological Mapping ◽  
Iron Formation ◽  
High Grade ◽  
Crystalline Core ◽  
High Grade Metamorphism ◽  
Iron Formations ◽  
Araçuaí Orogen ◽  
Southern Section

A área de estudo situa-se na parte sul do núcleo cristalino do Orógeno Araçuaí, próximo à fronteira com o Orógeno Ribeira. A característica fundamental da região é a abundância de rochas de alto grau metamórfico, na transição de fácies anfibolito-granulito. Uma cobertura metassedimentar neoproterozóica é a unidade dominante e está representada por paragnaisse migmatítico, bandado, com intercalações de quartzito, formação ferrífera micácea e formação ferrífera maciça. Corpos de anfibolito, pegmatito e charnockito também ocorrem na área. A principal estrutura dúctil é a foliação (Sn) regional, paralela ao bandamento composicional do granada-biotita paragnaisse. Fraturas são abundantes no quartzito e formação ferrífera maciça. As formações ferríferas são ricas em magnetita e formam corpos lenticulares com espessura decamétrica a centimétrica, concordantes com o bandamento composicional do granada-biotita paragnaisse. Preliminarmente, interpreta-se a gênese dessas formações ferríferas como sedimentar, durante a deposição dos protolitos areno-pelíticos do paragnaisse.Palavras-chave: metamorfismo de alto grau, formação ferrífera, Orógeno Araçuaí. ABSTRACT: GEOLOGICAL MAPPING OF THE SERRA DOS TURVOS REGION, CARATINGA (MG), SOUTHERN SECTION OF THE ARAÇUAÍ OROGEN. The study area is located in the southern part of the crystalline core of the Araçuaí orogen, close to the boundary with the Ribeira orogen. The main feature of the region is the abundance of high-grade metamorphic rocks of the amphibolite-granulite facies transition. A Neoproterozoic sedimentary cover is the dominant unit in the area and consists of migmatitic banded paragneiss with intercalations of quartzite, mica-bearing iron formation and massive iron formation. Amphibolite, pegmatite and charnockite bodies are also found in the area. The main ductile structure is the regional foliation (Sn) which is parallel to the compositional banding of the garnet-biotite paragneiss. Fractures are abundant in the quartzite and massive iron formation. The iron formations form lenticular bodies ranging in thickness from centimeters to decameters, which are concordant to the banding and foliation of the garnet-biotite paragneiss. Accordingly to field data, a sedimentary genesis can be suggested for the iron formations.Keywords: high grade metamorphism, iron formation, Araçuaí Orogen

Graftonite in phosphatic iron formations associated with the mid-Proterozoic Gamsberg Zn-Pb deposit, Namaqua Province, South Africa

2002 ◽  
Vol 66 (6) ◽  
pp. 915-927 ◽  
Author(s):  
M. Stalder ◽  
A. Rozendaal
Keyword(s):  
South Africa ◽  
Base Metal ◽  
Host Rock ◽  
Sedimentary Environment ◽  
Amphibolite Facies ◽  
Iron Formation ◽  
Iron Meteorites ◽  
Fine Grained ◽  
Mineralizing Process ◽  
Iron Formations

Abstract Granular aggregates of fine-grained graftonite (Fe,Mn,Ca)3(PO4)2 and intergrown wolfeite (Fe,Mn)2(PO4)(OH) occur in amphibolite-facies metamorphosed iron formations associated with the Gamsberg Zn-Pb deposit, South Africa. To date, these minerals were believed to have limited parageneses, being essentially restricted to granitic pegmatites and iron meteorites. This paper is the first report of the occurrence of graftonite and wolfeite in a regionally metamorphosed, iron formation-hosted setting. The aggregates are found together with Mn- and Pb-rich apatite and calcian pyromorphite in a pristine unit of almost pure chemical precipitates, the origin of which is intimately linked to the base-metal mineralizing process. Evidence from Gamsberg supports previous studies conducted on pegmatite-hosted graftonites that a simple host rock mineralogy and geochemical prerequisites, such as high activities of Fe, Mn, Ca and a deficiency in F, exert a dominant control on the stabilization of these minerals. However, in a marine sedimentary environment, significant concentrations of phosphorus have to be precipitated to prevent stabilization of all the phosphorus as fluorapatite. The paucity of graftonite in such settings suggests that the combination of these requirements is only rarely achieved.

INDEX AND PROBABILITY MAPS OF OCCURRENCE OF IRON ORE DEPOSITS: A PROPOSED GEOPHYSICAL APPROACH DEVELOPED IN CURRAL NOVO DO PIAUÍ (PI) STATE – BRAZIL

2013 ◽  
Vol 31 (3) ◽  
pp. 365
Author(s):  
Enos Nobuo Sato ◽  
Teodoro Isnard Ribeiro De Almeida ◽  
Vilson Marques Dias ◽  
Jorge Kazuo Yamamoto ◽  
Francisco De Assis Cavallaro ◽  
...  
Keyword(s):  
Iron Ore ◽  
Target Selection ◽  
Ore Deposits ◽  
Geological Mapping ◽  
Iron Formation ◽  
Probability Of Occurrence ◽  
Iron Ore Deposits ◽  
Exploration Area ◽  
Host Rocks ◽  
Iron Formations

ABSTRACT. This article shows the results of the development of a procedure called TC-ASA index which is based on the contrast of magnetic and radiometric properties between host rocks and the mineralization, being interpreted as the probability of occurrence and defining ambience where iron formation to occur. It consists in subtracting the values of total count (TC) from the analytic signal (ASA), which are products of gammaspectrometry and magnetic methods, respectively. This index was applied to the actual data referring to the iron formations of Curral Novo do Piau´ı, where the main mineral is magnetite, thus characterized by high magnetic susceptibility and often associated with metabasic rocks. These rocks often present low concentration of radioactive elements, enabling the identification of geological environment with potential for occurrence of iron ore. The use of this procedure allowed for the reduction of the exploration area, providing a fast target selection for geological mapping, geochemistry and ground geophysics. In addition, it supplies with important elements that will assist mining companies in setting strategic priorities.Keywords: iron ore exploration, probability of occurrence maps, gammaspectrometry, magnetometry. RESUMO. Este trabalho mostra os resultados do desenvolvimento de um procedimento aqui denominado Índice TC-ASA que tem por base o contraste de propriedades magnéticas e radiométricas entre as rochas encaixantes e a mineralização, sendo interpretado como probabilidade de ocorrência e delimitando ambiências propícias a ocorrências de formações ferríferas. Tal procedimento consiste na subtração dos valores de contagem total (CT) dos valores do sinal analítico (ASA), que são produtos dos métodos geofísicos gamaespectrométrico e magnetométrico, respectivamente. Este índice foi aplicado a dados reais coletados nas formações ferríferas de Curral Novo do Piauí, cujo principal mineral é a magnetita, caracterizada pela suscetibilidade alta e frequentemente associada à metabásicas. Estas rochas normalmente têm baixa concentração de elementos radioativos, possibilitando a identificação de ambiências geológicas potenciais para ocorrencia deste tipo de minério. A utilização deste procedimento permitiu a diminuição da área de pesquisa em estudo de reconaissance proporcionando uma rápida seleção de alvos para mapeamento geológico, geoquímica e geofísica terrestre. Além disto, proporciona elementos importantes que auxiliam as empresas de exploração mineral na definição de suas prioridades estratégicas.Palavras-chave: prospecção de minério de ferro, mapas de probabilidade de ocorrência, gamaespectrometria, magnetometria.

scholarly journals Iron and Carbon Isotope Constraints on the Formation Pathway of Iron-Rich Carbonates within the Dagushan Iron Formation, North China Craton

Minerals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 94
Author(s):  
Xiaoxue Tong ◽  
Kaarel Mänd ◽  
Yuhao Li ◽  
Lianchang Zhang ◽  
Zidong Peng ◽  
...  
Keyword(s):  
Iron Reduction ◽  
Isotope Composition ◽  
Iron Formation ◽  
Banded Iron Formations ◽  
Organic C ◽  
Formation Pathway ◽  
Wide Range ◽  
Dissimilatory Iron Reduction ◽  
O Isotope ◽  
Iron Formations

Banded iron formations (BIFs) are enigmatic chemical sedimentary rocks that chronicle the geochemical and microbial cycling of iron and carbon in the Precambrian. However, the formation pathways of Fe carbonate, namely siderite, remain disputed. Here, we provide photomicrographs, Fe, C and O isotope of siderite, and organic C isotope of the whole rock from the ~2.52 Ga Dagushan BIF in the Anshan area, China, to discuss the origin of siderite. There are small magnetite grains that occur as inclusions within siderite, suggesting a diagenetic origin of the siderite. Moreover, the siderites have a wide range of iron isotope compositions (δ56FeSd) from −0.180‰ to +0.463‰, and a relatively negative C isotope composition (δ13CSd = −6.20‰ to −1.57‰). These results are compatible with the reduction of an Fe(III)-oxyhydroxide precursor to dissolved Fe(II) through microbial dissimilatory iron reduction (DIR) during early diagenesis. Partial reduction of the precursor and possible mixing with seawater Fe(II) could explain the presence of siderite with negative δ56Fe, while sustained reaction of residual Fe(III)-oxyhydroxide could have produced siderite with positive δ56Fe values. Bicarbonate derived from both DIR and seawater may have provided a C source for siderite formation. Our results suggest that microbial respiration played an important role in the formation of siderite in the late Archean Dagushan BIF.

Occurrence and genetic implications of hyalophane in manganese-rich iron-formation, Cuyuna Iron Range, Minnesota, USA

1994 ◽  
Vol 58 (392) ◽  
pp. 387-399 ◽  
Author(s):  
Peter L. McSwiggen ◽  
G. B. Morey ◽  
Jane M. Cleland
Keyword(s):  
Depositional Environment ◽  
Iron Formation ◽  
East Central ◽  
Early Proterozoic ◽  
Iron Range ◽  
The North ◽  
History Of ◽  
Ferromanganese Deposits ◽  
Iron Formations ◽  
Chemical Sediments

AbstractThe recent discovery of hyalophane [(K,Ba)Al1−2Si3−2O8] on the North range segment of the Early Proterozoic Cuyuna Iron Range of east-central Minnesota has shed new light on the depositional environment of these rocks. This Ba-feldspar occurs in a 10 m thick interval within the main iron-formation and typically contains between 8 and 26 mol.% celsian (BaAl2Si2O8). Its occurrence in several textural settings suggests that barium was being deposited at various stages in the paragenetic history of the iron-formation. Some of the hyalophane grains occur as the cores of micronodules, which are structurally similar to oolites or oncolites, but mineralogically are very complex. The hyalophane also occurs as rims on core grains of diverse mineral composition and as discrete phases in late crosscutting veins.Hyalophane, like other Ba-silicates, has a very restricted paragenesis. They are associated typically either with sedimentary manganese and ferromanganese deposits, or with Cu-Pb-Zn-Ba deposits. The presence of hyalophane in the Early Proterozoic manganiferous iron ores of east-central Minnesota casts doubt on the historic interpretation of these deposits as typical Superior-type sedimentary iron-formations and instead supports the view that these deposits, at least in part, consist of chemical sediments from a hydrothermal fumarolic system. The suggested involvement of a hydrothermal system is also supported by the occurrence of aegirine within the hyalophane-rich layer, and the occurrence of tourmalinites and Sr-rich baryte veins elsewhere in the Cuyuna North range.

Stratigraphic Evolution of Fine-Grained Submarine Fan Systems, Tanqua Depocenter, Karoo Basin, South Africa

2006 ◽  
Vol 76 (1) ◽  
pp. 20-40 ◽  
Author(s):  
D. M. Hodgson ◽  
S. S. Flint ◽  
D. Hodgetts ◽  
N. J. Drinkwater ◽  
E. P. Johannessen ◽  
...  
Keyword(s):  
South Africa ◽  
Submarine Fan ◽  
Fine Grained ◽  
Karoo Basin ◽  
Stratigraphic Evolution

Petrology of the Gillis Mountain pluton, Cape Breton Island, Nova Scotia

1981 ◽  
Vol 18 (2) ◽  
pp. 395-404 ◽  
Author(s):  
S. M. Barr ◽  
A. M. O'Beirne
Keyword(s):  
Hydrothermal Activity ◽  
Parent Magma ◽  
Metallic Elements ◽  
Cape Breton Island ◽  
Porphyritic Granite ◽  
Fine Grained ◽  
Cape Breton ◽  
Mineralization Processes ◽  
Devonian Age ◽  
Bulk Chemistry

The Gillis Mountain pluton is a small composite granitoid intrusion in southeastern Cape Breton Island. It is one of the few plutons of known Devonian age in Cape Breton Island and is particularly significant because of the presence of Cu–Mo mineralization with porphyry affinities. The pluton consists of three main phases (quartz monzodiorite, porphyritic granite, and fine-grained granite) with minor late dykes of granite, granitic porphyry, and aplite. These phases probably represent a differentiation sequence from an 'I-type' parent magma of calc-alkalic affinity. All phases have been affected by phyllic and possibly potassic alteration, presumably related to the mineralization processes. However, this hydrothermal activity appears to be little reflected in the bulk chemistry of the pluton, except possibly in increased barium content and large standard deviations in the metallic elements and sulphur.

Alteration, mineralization, and metamorphism in the area of the East South "C" ore zone, 24th level of the Dickenson mine, Red Lake, northwestern Ontario

1984 ◽  
Vol 21 (1) ◽  
pp. 35-52 ◽  
Author(s):  
Neil A. Mathieson ◽  
C. Jay Hodgson
Keyword(s):  
Volcanic Rocks ◽  
Fluid Pressure ◽  
Chemical Effect ◽  
Iron Formation ◽  
Mesoscopic Scale ◽  
Red Lake ◽  
Northwestern Ontario ◽  
Mineral Associations ◽  
Mineral Assemblages ◽  
Volcaniclastic Rocks

The area of the East South "C" (ESC) orebody of the Dickenson mine, Red Lake, consists of variably altered and mineralized basalt, basaltic volcaniclastic rocks, minor sulphidic iron formation, and a series of mainly postdeformation dykes. Except for the dykes, the rocks are in general well foliated. The macroscopic structural geometry of the stratiform rocks has been determined to a large extent by movement on schistosity-parallel faults.Three broad types of mineralization or alteration are recognized: an Na–Ca–Mg depletion with associated Fe–Mn enrichment controlled by primary permeable structures in basalt; a series of carbonate and quartz or "chert" veins emplaced into fissures; and auriferous silicified and sulphidized zones controlled by vein-filled fractures. The last is the main mineralization type in the ESC orebody on the 24th level of the mine, which was the focus of this study. Although all mineralization types occur within the mine, they are not directly associated either temporally or spatially on a mesoscopic scale. All, however, appear to have been overprinted by or formed synchronously with the amphibolite-facies metamorphism.A rich variety of metamorphic mineral assemblages occurs in the volcanic rocks because of the chemical effect of pre- or synmetamorphic hydrothermal alteration. These assemblages and the composition and mineral associations of arsenopyrite in the ESC orebody closely constrain the conditions of metamorphism to 520–540 °C and 3.8–4.2 kbar (380–420 MPa) fluid pressure.

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