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.

A Multistage Genetic Model for the Metamorphosed Mesoproterozoic Swartberg Base Metal Deposit, Aggeneys-Gamsberg Ore District, South Africa

2020 ◽  
Vol 115 (5) ◽  
pp. 1021-1054 ◽  
Author(s):  
Tarryn Kim Cawood ◽  
Abraham Rozendaal
Keyword(s):  
South Africa ◽  
Genetic Model ◽  
Close Association ◽  
Hydrothermal Activity ◽  
Iron Formation ◽  
Fine Grained ◽  
Clastic Sediments ◽  
Mineral Assemblages ◽  
Stage 1 ◽  
Ore District

Abstract The polymetamorphosed Swartberg Cu-Pb-Zn-Ag deposit in the Namaqua Metamorphic Province of South Africa is a major metal producer in the region, yet its genesis remains poorly understood. The deposit comprises several stratiform to stratabound units, namely the Lower Orebody and Dark Quartzite, the overlying Barite Unit, and the Upper Orebody, all of which are folded by an F2 isoclinal syncline and refolded by an open F3 synform. A discordant Garnet Quartzite unit surrounds the Upper Orebody in the F2 hinge, where it overprints the Lower Orebody and Barite Unit. The Lower Orebody comprises sulfidic, pelitic lenses with fine-grained pyrite, sphalerite, galena, and lesser pyrrhotite, hosted by sulfide-poor but magnetite- and barite-bearing siliceous rock. The overlying Barite Unit is poorly mineralized and grades from massive magnetite-barite close to the F2 hinge to distal laminated baritic schist and quartzite. The Dark Quartzite is the stratigraphic equivalent of the Lower Orebody and Barite Unit but comprises siliceous quartzite and schist, with lenses of conglomerate and minor Fe-Mn-Zn phases. The Upper Orebody displays rapid zonations from massive magnetite-rich iron formation in the F2 hinge, rich in coarse galena, pyrrhotite, and chalcopyrite, to sulfide-poor, magnetite-bearing schist and quartzite. The Garnet Quartzite is dominated by quartz and almandine garnet and mineralized with pyrite and chalcopyrite. Geochemical discriminant plots show that the Lower Orebody has a significant detrital component, whereas the Upper Orebody and Barite Unit are strongly zoned, with the greatest chemogenic component close to the F2 hinge. This corresponds to a deposit-scale metal zonation from the Cu-rich F2 hinge to more Pb- and then Zn-dominated areas. Mineral assemblages and paleoredox proxies suggest generally oxic conditions, with a more reduced signature close to the hinge and in the sulfidic Lower Orebody lenses. The Lower Orebody is interpreted as a mixed chemogenic-pelitic unit, with sulfides deposited on or near the seafloor during stage 1 hydrothermal activity. The sulfidic lenses formed from fine mud and clay deposited in quiet seafloor depressions, in which warm, dense, reducing, Pb-Zn-Ba–rich stage 1 brines accumulated, while the siliceous portions formed from higher-energy clastic sediments on aerated seafloor highs. The Barite Unit forms a baritic cap to the Lower Orebody, while the Dark Quartzite is their shallower-water equivalent. Thereafter, clastic sediment with lesser hydrothermal input was deposited during stage 2a exhalations, forming the poorly mineralized portions of the Upper Orebody. During stage 2b hydrothermal activity, hot Cu-Fe–rich fluids invaded part of the Upper Orebody, creating the highly chemogenic protolith to the well-mineralized, magnetite-rich portion. Associated hydrothermal alteration in a discordant subseafloor feeder zone created the Garnet Quartzite protolith. The F2 hinge thus corresponds closely to the original vent zone. Swartberg therefore resembles a deformed and metamorphosed Selwyn-type sedimentary exhalative deposit, with both proximal- (Upper Orebody, Garnet Quartzite) and distal-style (Lower Orebody) mineralization. The close association of these styles suggests that differences in the mineralizing fluids and depositional environment, rather than proximity to a vent, determine the deposit style.

Lithostratigraphy of the Sinqeni Formation, Pongola Supergroup, South Africa

2020 ◽  
Vol 123 (3) ◽  
pp. 399-420
Author(s):  
N. Hicks ◽  
D.J.C. Gold
Keyword(s):  
South Africa ◽  
Southern Africa ◽  
Iron Formation ◽  
Banded Iron Formation ◽  
Quartz Arenite ◽  
Uranium Mineralisation ◽  
Kwazulu Natal ◽  
Iron Formations

Abstract The Mesoarchaean Sinqeni Formation forms the lowermost unit of the predominantly sedimentary Mozaan Group (Pongola Supergroup) of southern Africa. The formation comprises a dominantly arenaceous succession, which can be subdivided into four members. A laterally discontinuous gold- and uranium-bearing conglomerate package (Denny Dalton Member) is commonly developed at the base of the formation. Overlying the basal conglomerates are two significant quartz arenite packages (Dipka, and Kwaaiman Members) which are separated by a ferruginous shale package (Vlakhoek Member) that locally hosts banded-iron formation. The formation is the most extensively exposed succession of the Mozaan Group, cropping out extensively in the Hartland region, as well as in multiple inliers from Amsterdam in the Mpumalanga to Nkandla in central KwaZulu-Natal, with further exposures in Eswatini. Subeconomic gold and uranium mineralisation occur sporadically within the conglomerates of the Denny Dalton Member, and have previously been mined from multiple occurrences in the White Mfolozi, Mhlatuze and Nkandla Inliers whilst many prospecting trenches are found in the conglomerates of the Hartland and Amsterdam areas. Gold has also briefly been exploited from ferruginous shales and iron formations of the Vlakhoek Member in the Altona area. Litho-correlative equivalents of the formation comprise the Mandeva Formation (White Mfolozi Inlier), Skurwerant Formation (Amsterdam region) and Mkaya Formation (Magudu region).

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>

Hardness Evolution and High Temperature Mechanical Properties of Laser Welded DP980 Steel Joints

2018 ◽  
Vol 37 (6) ◽  
pp. 587-595
Author(s):  
Zhandong Wan ◽  
Wei Guo ◽  
Qiang Jia ◽  
Lang Xu ◽  
Peng Peng
Keyword(s):  
Yield Strength ◽  
Energy Absorption ◽  
Base Metal ◽  
Welded Joint ◽  
Dynamic Strain ◽  
Minor Effect ◽  
Fiber Laser Welding ◽  
Fine Grained ◽  
High Temperature Mechanical Properties ◽  
A Minor

AbstractDP980 steels were joined using fiber laser welding. The welded joint was characterized in terms of hardness distribution and tensile behavior at room temperature, 150 ℃, and 300 ℃, respectively. The fine-grained martensite in supercritical heat affected zone (HAZ) resulted in the highest hardness (428 Hv), while the tempered martensite contributed to the hardness decreasing (‒31 Hv). Both the ultimate tensile strength and yield strength of the base metal and welded joint decreased at 150 ℃, and then increased at 300 ℃ due to dynamic strain aging (DSA). The welded joint exhibited slightly higher yield strength and lower elongation at all the test temperatures compared to base metal due to the hardened fusion zone. The energy absorption reduced slightly with increasing temperature both for base metal and welded joint, and the weld posed a minor effect on the energy absorption. Deformation was one of the requirements for DSA effect. DSA enhanced the hardness of base metal (+78 Hv) and softened zone (+53 Hv). HAZ was not softened enough to become the weakest position during tensile test.

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.

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.

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