The Separation of Carbonaceous Matter from Refractory Gold Ore Using Multi-Stage Flotation: A Case Study

As a pre-treatment method of refractory gold ore, carbonaceous matter (C-matter) flotation was investigated with multi-stage flotation by rougher, scavenger, and cleaner stages. Different dosages of kerosene and MIBC (4-Methyl-2-pentanol) were applied and the optimum dosage was selected by testing in each flotation stage. With the combination of each stage, four circuit designs were suggested, which were a single-stage rougher flotation (R), rougher-scavenger flotation (R+S), rougher-scavenger-scavenger cleaner flotation (R+S+SC), and rougher-rougher cleaner-scavenger-scavenger cleaner flotations (R+S+RC+SC). The results indicated that the scavenger flotation increased C-matter recovery but reduced C-matter grade compared with single-stage rougher flotation. Cleaning of the scavenger flotation concentrate improved C-matter grade significantly, but reduced recovery slightly. Cleaning of the rougher flotation concentrate achieved overall improved selectivity in flotation. A combination of rougher-scavenger flotation followed by cleaning of both concentrates (R+S+RC+SC) resulted in 73% C-matter recovery and a combined cleaner concentrate grade of 4%; the final tailings C-matter grade was 0.9%, where the C-matter remaining in the tailings was locked, and fine grained. The results demonstrate the need for the multi-stage flotation of C-matter from refractory gold ore to achieve selective separation and suggested the potential of C-matter flotation as the pre-treatment for efficient gold production.

Significance of Acid Washing after Biooxidation of Sulfides in Sequential Biotreatment of Double Refractory Gold Ore from the Syama Mine, Mali

Environmentally friendly pretreatment of double refractory gold ores (DRGO) to improve gold recovery without emitting pollutant gas is challenging. Sequential biotreatment, including iron-oxidizing microorganisms to decompose sulfides, followed by the enzymatic decomposition of carbonaceous matter, was recently developed. The effect of acid washing by 1 M HCl for 24 h between two bioprocesses was evaluated using a real double refractory gold ore from the Syama mines, Mali, which includes 24 g/t of Au and 5.27 wt % of carbon with a relatively higher graphitic degree. The addition of the acid washing process significantly improved gold recovery by cyanidation to yield to 84.9 ± 0.7% from 64.4 ± 9.2% (n = 2). The positive effects of acid washing can be explained by chemical alteration of carbonaceous matter to facilitate the accessibility for lignin peroxidase (LiP) and manganese peroxidase (MnP) in cell-free spent medium (CFSM), although the agglomeration was enhanced by an acid attack to structural Fe(III) in clay minerals. Sequential treatment of DRGO basically consists of the oxidative dissolution of sulfides and the degradation of carbonaceous matter prior to the extraction of gold; however, the details should be modified depending on the elemental and mineralogical compositions and the graphitic degree of carbonaceous matter.

Thorium, uranium and rare earth mineralization in rocks of the Ugakhan gold deposit, Bodaibo ore region (Irkutsk oblast)

The paper reports on the results of studies of ore-bearing rocks of the Ugakhan gold deposit (Bodaybo district): metasandstones, metasiltstones and carbonaceous shales. The rocks consist of quartz, feldspar (albite, orthoclase), Fe-Mg chlorite, mica (muscovite, sericite) and carbonates (calcite, dolomite, anker-ite) and accessory titanite, rutile, tourmaline, zircon and apatite. All rocks contain fragments of microfossils exhibiting striking concentric zonation with alternated dark (carbonaceous matter) and light (carbonate-mica material) layers. In a range from metasandstones to carbonaceous shales, the rocks exhibit an increase in mica amount and the content (up to 3%) of carbonaceous matter, as well as the formation of regeneration rims around relict tourmaline and zircon. The REE mineralization includes silicates (REE-bearing epidote, thorite), fuorocarbonates (bastnesite) and phosphates (monazite, xenotime, ankylite), which are closely related to U minerals (uraninite, cofnite). Bastnesite, ankylite and thorite formed due to the decomposition of earlier REE-bearing epidote, whereas monazite and xenotime are the products of decomposition of apatite. Uraninite formed during lithifcation of matrix of carbon-bearing rocks and is replaced by cofnite. The thermal analysis of carbonaceous matter and the formation temperature of chlorite calculated using chlorite geothermometer (296–371 °С) indicate the transformation of rocks under conditions of sericite-chlorite subfacies of greenschist facies of metamorphism.

Flotation of Carbonaceous Matter from a Double Refractory Gold Ore: The Effect of MIBC on Flotation Performance and Kinetics

The use of alkaline pressure oxidation to pretreat refractory gold ore often results in insufficient gold recovery (<60%) in downstream thiosulfate leaching. To improve gold recovery, flotation was considered for the separation of carbonaceous matter (C-matter). In this study, the effect of MIBC on C-matter flotation was investigated to understand the role of the frother in bubble and froth formation and on flotation kinetics. MIBC dosages between 30 and 150 g/t were used in combination with 500 g/t of kerosene as a collector. The results showed that the recovery and selectivity of C-matter were improved with increasing MIBC dosages. Improved selectivity at higher MIBC dosages was attributed to faster C-matter recovery as bubble size decreased to the critical coalescence concentration (CCC) and to changes to the foam structure. Analysis of flotation kinetics showed that the flotation rate increased as the MIBC dosage increased due to the decreasing bubble size and the reduced induction time caused by the interaction between the collector and the frother. The results of this study explain the role of MIBC in C-matter flotation and can be used as a design basis for scavenger-cleaner flotation testing. Overall, the results show the potential for flotation as a means to improve gold recovery in thiosulfate leaching through the removal of C-matter.

Black Agates from Paleoproterozoic Pillow Lavas (Onega Basin, Karelian Craton, NE Russia): Mineralogy and Proposed Origin

The present study provides the first detailed investigation of black agates occurring in volcanic rocks of the Zaonega Formation within the Onega Basin (Karelian Craton, Fennoscandian Shield). Three characteristic texture types of black agates were identified: monocentric concentrically zoning agates, polycentric spherulitic agates, and moss agates. The silica matrix of black agates is only composed of length-fast and zebraic chalcedony, micro- and macro-crystalline quartz, and quartzine. In addition to silica minerals, calcite, chlorite, feldspar, sulphides, and carbonaceous matter were also recognised. The black colour of agates is related to the presence of disseminated carbonaceous matter (CM) with a bulk content of less than 1 wt.%. Raman spectroscopy revealed that CM from black agates might be attributed to poorly ordered CM. The metamorphic temperature for CM from moss and spherulitic agates was determined to be close to 330 °C, whereas CM from concentrically zoning agates is characterised by a lower temperature, 264 °C. The potential source of CM in moss and spherulitic agates is associated with the hydrothermal fluids enriched in CM incorporated from underlaying carbon-bearing shungite rocks. The concentrically zoning agates contained heterogeneous CM originated both from the inter-pillow matrix and/or hydrothermal fluids.

Provenance and depositional characteristics of Lathi Formation in southern part of Jaisalmer Basin: Implications for exploration of sandstone type uranium mineralization

The lower Jurassic Lathi Formation covers about 900 sq. km area and forms the lowermost unit of Jaisalmer Basin of western Rajasthan. Lithologically the Lathi Formation comprises of conglomerate, sandstone, siltstone, shale and mudstone. The sandstones are generally medium- to coarse-grained, moderately sorted and show variation in colour, grain-size and texture. Petrographic studies indicate a mixed provenance for the Lathi sandstone. On the basis of geochemical data, theses sandstones are classified into sub-arkose, litharenite and sub-litharenite. Palaeo-weathering indices such as CIA (80.45), CIW (85.23) and PIA (84.23) suggest moderate to high degree of chemical weathering of the source area, intermediate and felsic igneous provenance, under humid to semi-humid climatic conditions. Further, the geochemical data indicate the sedimentation in a passive continental margin setting. The Bouguer gravity image clearly depicts the north westward slope of the basement. Modelling studies of the gravity data revealed average depth to the basement as 800m, 400m and 250m respectively in northwest, central and southeastern parts of the surveyed area. Exploration activities by Atomic Minerals Directorate for Exploration and Research have resulted in location of several uranium anomalies in the Lathi Formation. Lathi Formation is characterised by many favourable parameters such as fertile provenance, arkosic sandstones intercalated with shale/mudstone, reduced sedimentary facies with carbonaceous matter, lignite and pyrite deposited in continental to marginal marine environment. Malani Igneous Suit and metamorphic rocks constitute the basement for Jaisalmer Basin. Malani rhyolites and granites are fertile source of uranium, containing 6.7 ppm and 9.2 ppm average and intrinsic uranium respectively. Presence of carbonaceous matter and pyrite bearing sandstones, indicative of reducing environment at depth below water table (R.L. 150 m), was reported during subsurface exploration in Lathi sandstone which is a favourable condition for Lathi sediments to host uranium mineralization.

Petro-mineralogical and geochemical characteristics of Shahaba Limestone from Gogi-Kanchankayi sector, Bhima Basin, Karnataka with reference to Uranium mineralisation

The Shahabad Limestone Formation of Bhima Basin from Gogi-Kanchankayi area occurs in heterogeneous forms like massive/blocky limestone, argillaceous/ siliceous limestone and laminated/ flaggy limestone. These limestones are primarily composed of micrite, which often alters into sparry calcite on diagenesis with associated impurities of quartz, feldspar, barite, chlorite, glauconite, sulphides and carbonaceous matter. Geochemically, these limestones comprises of variable CaO with low MgO and P2O5 content. Trace elements concentration shows elevated Ba, Rb and depleted Sr. The current study classified these limestones as non-dolomitic and non-phosphatic types deposited in shallow marine carbonate platform setting with low energy conditions. Post-sedimentation, basin tectonics has resulted in reactivation of the basin margin fault causing intense fracturing of limestone. Subsequent hydrothermal movement along those fractures has resulted in re-mobilisation and re-precipitation of sulphides and carbonaceous matter, and along with alteration has facilitated the precipitation of the uranium bearing minerals.

Facies Architecture and Sedimentary Structures in the drill cores of Uranium Bearing Sediments of Banganapalle Formation of Palnad Sub-basin, Guntur District, Andhra Pradesh

The Banganapalle Formation, the lowest member of the Neoproterozoic Kurnool Group of rocks, resting over the basement granites, has been identified as the host rock for uranium in Koppunuru area in the western part of Palnad sub-basin. The uppermost arenite facies of the Banganapalle Formation is exposed on surface and shows only few bedform indicators like ripple marks, planer laminations etc. Down-hole lithological examinations on course of core drilling in Koppunuru and adjoining areas identified five recognizable lithofacies of Banganapalle Formation, viz. basal conglomerate unit, quartzite-shale intercalated facies, and two quartz arenite facies separated by a grey shale dominated argillaceous facies. The polymictic conglomerate, with unsorted grit to pebble size clasts of granite, shale, quartzite, vein quartz and dolerite indicate short distance transportation and derivation from nearby granitoids traversed by quartz reef/dolerite dykes. Cyclic repetitions of arenaceous and argillaceous sediments in Banganapalle lithocolumn above the basal conglomerates point to alternate rhythmic marine transgression and regression regimes. These units can also be discriminated based on their sedimentary texture, bedforms and several soft-sedimentary penecontemporaneous deformational structures (PCD) like load structure, convolute bedding/laminations, and slump structures such as micro-slips, gravity faults and folds. These syn-sedimentary structures clearly indicate perturbation and submergence of the basin contemporaneous to deposition. Cross-beds suggests change in current direction/intensity while bi-directional symmetrical ripples in outcrops of upper arenite facies suggests that the Banganapalle sediments are derived from the basement granitoids exposed to the north as well as upper Cuddapah sediments to its west. Overall, the sedimentary structures, textural and composition variation of the lithounits suggest deposition of these sediments in marginal marine, inter- to supra-tidal flat environment. The porous and permeable nature of the quartz arenite and the basal conglomerates and the presence of available reductants in the form of sulphides and carbonaceous matter make them the best suited loci for fluid movement and precipitation of uranium.