Zn Grade Research Articles

Flotation of zinc oxide ores by cationic and mixed collectors

The flotation of smithsonite from tailing which comes from the cerussite flotation circuit was investigated using Armac C and Armac T as amine collectors. The results indicated that the dosage of sodium sulfide, collector type, and desliming are the main affecting factors on the Zn grade and recovery of smithsonite flotation concentrate. Armac T acts a little more selectively than Armac C, and enhances the Zn grade of the concentrate, while Armac C improves the recovery of Zn. At the mixture ratio of Armac C:Armac T=1:6, without consumption of any gangue depressants, an optimal concentrate with 94.4% recovery, and 42.3% Zn grade is obtained. In this condition, the collectors’ consumption is decreased significantly. Desliming prior to flotation is essential for successful recovery of smithsonite.

Delineation of mineralization zones using concentration–volume fractal method in Pb–Zn carbonate hosted deposits

This study uses the C–V fractal model to separate mineralization zones especially enriched supergene and hypogene protore in an Iranian Pb–Zn carbonate hosted deposit, based on subsurface data. The Tangedezan deposit is located in central Iran. In order to separate the two major mineralization zones in this deposit, log–log plots of major elements are prepared, which are fitted straight lines that show C–V relationship for Pb, Zn, Ag and Cd especially in NE of the area. Based on power–law relationship between elemental concentrations and their host rock volume, the oxidation and sulfidation zones are separated. Log–log plots for the mentioned elements show three mineralization zones including enriched supergene (oxidation), hypogene sulfide protore and low mineralization zones. The obtained results were compared with geological zonation model. This comparison shows that the interpreted zones by the C–V fractal model are in agreement with the proposed geological model. The C–V log–log plot for Zn reveals that there is an enriched supergene zone (oxidation), which separates out at the Zn grade of 13.8% in Tangedezan deposit. The high sulfide zone (hypogene protore) interpreted to have 7.2% to 13.8% and the low mineralization zone, mainly consisting of low sulfidation and to lesser extent low oxidation, has less than 7.2% of Zn grade in the deposit.

Cu–(Ni–Co–Au)-bearing massive sulfide deposits associated with mafic–ultramafic rocks of the Main Urals Fault, South Urals: Geological structures, ore textural and mineralogical features, comparison with modern analogs

Cu-rich massive sulfide deposits associated with mafic–ultramafic rocks in the southern portion of the Main Urals Fault (MUF) are characterized by variable enrichments in Ni (up to 0.45wt.%), Co (up to 10wt.%) and Au (up to 16ppm in individual hand-specimens). The Cu (Ni–Co)-rich composition of MUF deposits, as opposed to the Cu (Zn)-rich composition of more eastward massive sulfide deposits of broadly similar age along the western flank of the Magnitogorsk arc, reflects the abundance of seafloor-exposed, Ni–Co-rich ultramafic rocks in the most external portion of the Early-Devonian Magnitogorsk forearc. Morphological, textural, and compositional differences between individual deposits are interpreted to be the result of the sulfide deposition style and, in part, of the original subseafloor lithology. One deposit produced by dominantly on-seafloor hydrothermal processes is characterized by pyrite–marcasite≫pyrrhotite, not so low Zn grades (occasionally up to 2wt.%), abundant clastic facies and periodical superficial oxidation. Deposits produced by dominantly subseafloor hydrothermal processes are characterized by pyrrhotite>pyrite, very low Zn (generally < to ≪0.1wt.%), volumetrically minor clastic facies, and multi-layer deposit morphology. Very low Ni/Co ratios in the on-seafloor deposit may indicate a dominant metal contribution from a mafic rather than ultramafic source. The sulfide mineralization was associated with extensive hydrothermal alteration of the host ultramafic and mafic rocks, leading to formation of abundant talc, talc–carbonate and chlorite rocks. Occurrence of large volumes of such altered lithotypes in ophiolitic belts may be considered as a potential searching criteria for MUF-type (Cu, Co, Ni)-deposits. In spite of the contrasting geodynamic environment, geological, geochemical, textural and mineralogical peculiarities of the MUF deposits in many respects are similar to those of ultramafic-hosted massive sulfide deposits along the Mid-Atlantic Ridge. In geological time, supra subduction-zone settings appear to have been more effective than mid-ocean ridge settings for preservation of ultramafic-hosted massive sulfide deposits.

Study on the Integrative Utilization of Cyanide Tailings of Polymetallic Sulfide Ore of Gold and Silver

In this paper, based on the experiment on pure minerals, namely, galena, sphalerite and pyrite, it is concluded that the appropriate pH range for galena flotation is 8.5-10.5, that for sphalerite flotation is 7-10.5 and for pyrite is 2.5-6.5. For galena, sphalerite and pyrite, butyl xanthate has a better collecting performance than ammonium dibutyl dithiophosphate. Both Na2SO3 and ZnSO4 have a relatively weak inhibitory effect on galena. As for sphalerite, the mixing of Na2SO3 and ZnSO4 has a better inhibitory effect than when they are used alone, with the best inhibitory effect obtained when the proportion of Na2SO3 and ZnSO4 is 1:2 and their dosages are respectively 100mg/L and 200mg/L. In zinc flotation, CuSO4 demonstrates an apparent activating effect on the inhibited sphalerite with its appropriate dosage at 2*10 -4 mol/L. In actual separation and selection of ore, when the grades of lead, zinc and silver in cyanide tailings are respectively 2.41%, 3.77% and 272g/t, a fairly good index is obtained where the Pb concentrate is of a grade of 33.41% with its silver grade of 4051.57g/t and the grade of Zn concentrate is 59.67% with its silver grade of 798.08g/t.

Improving the selective flotation of jamesonite using tannin extract

Five tannin extracts from different trees were used to improve jamesonite flotation in the Changpo plant in Nandan, China. The flotation results demonstrated that the larch tannin extract was the best for improving jamesonite flotation. Compared to flotation without larch tannin extract, industrial trial results indicated that the Sb and Pb grade in the final concentrate increased from 13.1% and 14.8% to 17.6% and 19.9%, respectively, as the Zn grade decreased from 9.1 to 6.5%. In addition, the Sb and Pb recovery of 84.5% was achieved with the larch tannin extract (84.2% without larch tannin extract). Larch tannin extract depressed not only marmatite, but also to some extent pyrrhotite, arsenopyrite, pyrite, calcite and quartz.

The Preliminary Investigation of Low Grade Zinc Oxide Ore

Flotation is a conventional way for treating low grade metal oxide ore which has some advantages such as high efficiency and low cost. In order to recover the zinc from a low grade complex zinc oxide ore in which the grade of Zn is 13 wt.%, this paper presents a preliminary investigation of this type of ore by flotation method. In the experiments, the effects of different parameters such as grinding fineness, amount of Na2SiO3, amount of Na2S and amount of octadecylamine were investigated in relation to the metal contents of concentrates. The results show that about 35% of initial Zn content was obtained with 70% -200 mesh grinding fineness, 1000g/t Na2SiO3, 2000g/t Na2S and 500g/t octadecylamine. It is clear that the preliminary flotation tests with the ore sample indicated that there was no selectivity in terms of zinc recovery. Almost 65% zinc remained in the tailings and could not be recovered by flotation due to its complicated mineralogical structure. Therefore, application of metallurgical processes is proposed for zinc recovery from the tailings in the following investigations.

Hydrometallurgical Treatment of Low Grade Zinc Oxide Ore

In this research, a leaching study was carried out to assess the effect of several parameters on zinc extraction in a low grade complex zinc oxide ore in which the grade of Zn is 13 wt.%, and 52.8% of Zn is contained in siderite, 34.63% in limonite and 11.55% in smithsonite. The influencing parameters investigated include sulfuric acid concentration, reaction temperature, reaction time and liquid to solid ratio (L/S). The results show that over 90% of Zn can be extracted from the low grade complex zinc oxide ore when the leaching process is operated in 2M sulfuric acid at 60°C for 2.5h with a liquid to solid ratio of 6:1.

Alkaline Leaching of Low Grade Complex Zinc Oxide Ore

Alkaline leaching is an important way for treating low grade metal oxide ore, which has some advantages such as low corrosion and low pollution compared to acidic leaching. In order to recover the zinc from a low grade complex zinc oxide ore in which the grade of Zn and Fe are 13 wt.% and 40.2 wt.%, respectively, and 52.8% of Zn is contained in siderite, 34.63% in limonite and 11.55% in smithsonite, this paper presents a preliminary investigation of this type of ore by alkaline leaching method. In this study, ammonia-ammonium chloride and ammonia-ammonium carbonate were used as the leaching reagents. The effects of alkaline concentration, leaching time, leaching temperature and liquid to solid ratio (L/S) were studied, respectively. The results show that 43.15% of initial Zn content was extracted adopting ammonia-ammonium chloride as the leaching reagent in 4.5M at 30°C for 3h with a liquid to solid ratio of 4:1, while 43.07% of Zn recovery was achieved employing ammonia-ammonium carbonate as the leaching reagent at 5M, 30°C and 4:1(L/S). The low leaching rate of Zn is probably attributed to that the zinc contained in siderite was not extracted completely because Zn and Fe exist as isomorphism in siderite.

REE and C‐O Isotopic Geochemistry of Calcites from the World‐class Huize Pb‐Zn Deposits, Yunnan, China: Implications for the Ore Genesis

Abstract:The world‐class Huize Pb‐Zn deposits of Yunnan province, in southwestern China, located in the center of the Sichuan‐Yunnan‐Guizhou Pb‐Zn polymetallic metallogenic province, has Pb+Zn reserves of more than 5 million tons at Pb+Zn grade of higher than 25% and contains abundant associated metals, such as Ag, Ge, Cd, and Ga. The deposits are hosted in the Lower Carboniferous carbonate strata and the Permian Emeishan basalts which distributed in the northern and southwestern parts of the orefield. Calcite is the only gangue mineral in the primary ores of the deposits and can be classified into three types, namely lumpy, patch and vein calcites in accordance with their occurrence. There is not intercalated contact between calcite and ore minerals and among the three types of calcite, indicating that they are the same ore‐forming age with different stages and its forming sequence is from lumpy to patch to vein calcites.This paper presents the rare earth element (REE) and C‐O isotopic compositions of calcites in the Huize Pb‐Zn deposits. From lumpy to patch to vein calcites, REE contents decrease as LREE/HREE ratios increase. The chondrite‐normalized REE patterns of the three types of calcites are characterized by LREE‐rich shaped, in which the lumpy calcite shows (La)N &lt; (Ce)N &lt; (Pr)N≈ (Nd)N with Eu/Eu* &lt; 1, the patch calcite has (La)N &lt; (Ce)N &lt; (Pr)N≈ (Nd)N with Eu/Eu* &gt; 1, and the vein calcite displays (La)N &gt; (Ce)N &gt; (Pr)N &gt; (Nd)N with Eu/Eu* &gt; 1. The REE geochemistry of the three types of calcite is different from those of the strata of various age and Permian Emeishan basalt exposed in the orefield. The δ13CPDB and δ18OSMOW values of the three types of calcites vary from −3.5‰ to −2.1‰ and 16.7‰ to 18.6‰, respectively, falling within a small field between primary mantle and marine carbonate in the δ13CPDB vs δ18OSMOW diagram.Various lines of evidence demonstrate that the three types of calcites in the deposits are produced from the same source with different stages. The ore‐forming fluids of the deposits resulted from crustal‐mantle mixing processes, in which the mantle‐derived fluid components might be formed from degassing of mantle or/and magmatism of the Permian Emeishan basalts, and the crustal fluid was mainly provided by carbonate strata in the orefield. The ore‐forming fluids in the deposits were homogenized before mineralization, and the ore‐forming environment varied from relatively reducing to oxidizing.

Process optimization and modelling of sphalerite flotation from a low-grade Zn-Pb ore using response surface methodology

In this research sphalerite flotation from a low-grade lead-zinc ore containing 3% Zn and 1% Pb was studied. Three control parameters including activator (CuSO 4) dosage, collector (potassium amyl xanthate (PAX)) dosage and pH, each in five levels, were investigated. Response surface methodology (RSM) was implemented for statistical design and analysis of experiments and process modelling. Four quadratic mathematical models were derived for prediction of Zn grade, Zn recovery, Zn separation efficiency and Pb recovery. Analysis of variance showed that collector dosage was the most significant factor affecting Zn recovery and separation efficiency. In process optimization, maximum values of Zn recovery and separation efficiency were achieved as 79.12% and 64.59%, respectively. Using CuSO 4 concentration of 150 g/t, PAX dosage of 120 g/t, and pH of 10.4, Zn recovery of 61.5% and separation efficiency of 51.49% were obtained. However, in optimization studies, a case proposed by the model in which using the same consumption of reagents, Zn recovery and separation efficiency were improved about 9% and 5%, respectively. This study showed that RSM could effectively be applied for the modelling of flotation process and for finding an economical optimum condition to achieve maximum separation efficiency under minimum consumption of flotation reagents.

Depression of pyrite in the flotation of high pyrite low-grade lead–zinc ore using Acidithiobacillus ferrooxidans

In this research work, selective depression of pyrite in the flotation of a low-grade lead–zinc ore containing 31% pyrite was investigated in the absence and presence of Acidithiobacillus ferrooxidans. Pyrite was significantly depressed with these bacteria using the optimum dosage of reagents. Sphalerite recovery and Zn grade in the obtained sphalerite concentrate were both enhanced by bacteria. The results of bioflotation experiments showed that bacterial depression of pyrite is very sensitive to the concentration of other flotation reagents. Least significance difference (LSD) bars were used to study the significance of the factors under study with a confidence interval of 90%. Under similar conditions, A. ferrooxidans was seen to increase the Zn grade and separation efficiency more effectively than sodium cyanide. Flotation kinetic studies confirmed a considerable decrease in the pyrite kinetic rate constant in the presence of A. ferrooxidans.

Rb-Sr isotopic dating of sphalerite from the giant Huize Zn-Pb ore field, Yunnan Province, Southwestern China

The giant Huize Zn-Pb ore field in Yunnan Province, southwestern China, comprises the Qilinchang and Kuangshanchang deposits. The deposits are large in scale (more than 5 Mt of Zn and Pb) and high in grade (average grade of total Zn and Pb is 30%). Reported in this paper are the results of Rb-Sr isotopic dating of sphalerite from this ore field. Two precise ages (223.5±3.9 Ma and 226±6.4 Ma) have been obtained from two isochrons. These two ages are close to the reported ages of native copper mineralizations related to the Emeishan flood basalts in this region, which are 226 Ma to 228 Ma. Previous studies showed that the magnitude of uplift resultant from the Emeishan flood basalts is greater than 1000 m, indicating that the Kuangshanchang and Qilinchang deposits were formed during the same geological event and originated by fluid migration during uplifting resultant from the Emeishan flood basalts.

Rhyolite Geochemical Signatures and Association with Volcanogenic Massive Sulfide Deposits: Examples from the Abitibi Belt, Canada

The relationship between rhyolite geochemistry and volcanogenic massive sulfide (VMS) mineralization has been proposed as an exploration tool to discriminate prospective felsic volcanic centers. The most widely used classification discriminates between four types of rhyolite: FI, FII, FIIIa, and FIIIb. The FI rhyolites are calc-alkaline, with strongly fractionated REE patterns and strongly negative Ta and Nb anomalies. They are usually considered barren, unless associated with FII or FIII felsic volcanic rocks. The FII rhyolites are calc-alkaline to transitional with moderately fractionated REE patterns and moderate Ta and Nb anomalies. They range from barren to having a high potential to host VMS mineralization. The FIIIa and FIIIb rhyolites are tholeiitic and show weakly fractionated REE patterns and weak to absent Nb and Ta anomalies. They have the highest potential to host VMS mineralization. The FIIIb rhyolites are high-temperature rhyolites with flat REE patterns and no Ta or Nb anomalies. The Abitibi greenstone belt, especially in Quebec, is well known for its abundant and diverse VMS deposits. Representative samples of VMS-associated rhyolites within and outside of mining districts, including the classic Noranda VMS district, were analyzed for major and trace elements to validate their proposed favorability for hosting VMS deposits. Results indicate that all of the rhyolite types are prospective, but mineralization may differ from the classic Noranda-type VMS deposit. The FI-type rhyolites appear to be particularly associated with gold-rich VMS deposits, such as the world-class Laronde deposit, and are more prospective for Cu-Au replacement and vein-type deposits. The FII-type rhyolites account for about 70 percent of rhyolites in the Abitibi belt. Although considered less prospective, some districts dominated by FII rhyolites, such as Val-d’Or and Selbaie, have collectively produced in excess of 100 million metric tons (Mt) of ore. Deposits in these districts mainly consist of sulfide veins and disseminated ore with low Cu and Zn grades and are associated with abundant and highly vesicular volcaniclastic rocks that display a compositional continuum from andesite to rhyolite. Other weakly mineralized FII districts (e.g., Hunter mine, Gemini-Turgeon) are characterized instead by bimodal flow-dome sequences. The FIIIa-type rhyolites occur mainly in the Noranda district and form flow-dome complexes in bimodal sequences with associated Noranda-type VMS mineralization. In small felsic centers (Joutel, Normetal, Chibougamau, Quevillon) that show a volcanic evolution from FIIIa to FII to FI affinities, VMS deposits are directly associated with FIIIa rhyolites, thus demonstrating the usefulness of rhyolite geochemistry for exploration in these areas. The FIIIb rhyolites are rare in the Abitibi belt, with most occurring in the Matagami district where they are associated with Zn-Cu VMS deposits. Based on this analysis, we suggest that a combination of rhyolite geochemistry, volcanic facies, and style of the mineralization may be more meaningfully applied in exploration than rhyolite type alone, particularly in the case of FI and FII rhyolites.

Improvement of flotation behavior of Mengzi lead-silver-zinc ore by pulp potential control flotation

The electrochemical behavior of Mengzi lead-silver-zinc ore flotation system was studied. Based on the electrochemical characteristics of sulfide mineral flotation system, a stage potential control flotation was developed with the main parameters of pulp potential( Φ p), pH value and collector dosage. Using N, N' diphenylamino-dithiolphosphoric acid(NNDDC) as a collector, which has good selectivity for galena flotation at pH 8.8 and pulp potential 330 mV, DDTC is used as secondary collector to improve both the grade and recovery of Pb and Ag. The pulp potential values significantly influence the floatability of practical minerals and single minerals when using NNDDC as the collector. The flotation recovery of galena reaches 85% at about 0.3 V and pH8.8. With the usage of pulp potential control during grinding and flotation, the new pulp electrochemical technology for Mengzi lead-silver-zinc ore flotation was developed. The results show that the grades of Pb and Ag of galena concentrate are 55% and 1 800 g/t, respectively, while the recoveries of Pb and Ag are 86.5% and 65%, respectively, the grade of Zn of marmatite concentrate is 42.5%, and the recovery of Zn is 91.25%.

The LaRonde Penna World-Class Au-Rich Volcanogenic Massive Sulfide Deposit, Abitibi, Quebec: Mineralogy and Geochemistry of Alteration and Implications for Genesis and Exploration

Gold-rich volcanogenic massive sulfide (VMS) deposits consist of synvolcanic banded and concordant massive sulfide lenses and adjacent stockwork feeder zones in which gold concentration in g/t Au exceeds the combined Cu, Pb, Zn grades in wt percent and thus constitutes the main commodity. The Agnico-Eagle LaRonde Penna deposit is a world-class Au-rich VMS (production, reserves and resources of 58.8 Mt at 4.31 g/t Au) located in the eastern part of the Blake River Group of the Abitibi greenstone belt. The deposit comprises four stacked massive sulfide lenses within the upper member of the Bousquet Formation (2698–2697 Ma). The two main ore zones, 20 North and 20 South, are sheetlike, massive to semimassive polymetallic sulfide lenses and stringer zones. Both lenses and sulfide stringers are deformed and transposed by the main foliation. The 20 North lens (Zn-Au-Ag-Cu-Pb) is the main orebody. It is subdivided into two zones: the 20N Au and 20N Zn zones. The 20N Au zone is a transposed and ribbon-textured gold- and copper-rich pyrite-chalcopyrite stringer zone overlain to the south by a 10- to 30-m-thick massive pyrite-sphalerite-galena lens (20N Zn zone). The 20 South lens is an 8- to 10-m-thick gold- and zinc-rich massive sulfide and stringer zone located about 10 to 15 m below the Cadillac Group sedimentary rocks (<2687 Ma). At depth (≥1,900 m below surface), the 20 North and 20 South lenses grade into aluminous zones composed mainly of quartz-pyrite-kyanite-andalusite-muscovite-Zn–rich staurolite assemblages that host transposed sulfide stringers and local semimassive to massive Au-rich pyrite and chalcopyrite layers. The synvolcanic hydrothermal alteration now corresponds to mappable upper greenschist-lower amphibo-lite–grade metamorphic assemblages. The footwall of the 20 North lens is characterized by a large discordant to semiconformable distal quartz-biotite ± garnet assemblage, which transitions laterally into a proximal quartz-garnet-biotite-muscovite zone. The abundance of pink Mn-rich garnet porphyroblasts increases toward the 20N Au zone. The hanging wall of the 20 North lens is characterized by a meter-thick zone of fracture-controlled pink alteration composed of quartz, biotite, rutile and/or anatase, and titanite associated with barren sulfide stringers. The garnet-rich assemblage in the footwall records gains in MnO, Fe2O3(total), and MgO and losses of Na2O. In the hanging wall, Fe2O3(total), S, and CO2 were added to the rocks with a slight increase in K2O, and CaO. At depth (≥ 1,900 m), the Au-rich aluminous replacement zone is a (up to 30 m) thick, highly strained zone composed of a quartz-pyrite-kyanite-andalusite-chalcopyrite-gold assemblage. All oxides except Al2O3, SiO2, and Fe2O3(total) were strongly leached. The metamorphosed hydrothermal alteration associated with the 20 South lens is characterized by a pink quartz-biotite-rutile-titanite assemblage very similar to that in the hanging wall of the 20 North lens. Toward the ore zone, the pink assemblage is gradually replaced by a proximal quartz-muscovite-green mica-pyrite assemblage, which hosts the sulfide mineralization. The aluminous alteration at LaRonde Penna is interpreted to be the metamorphic equivalent of an advanced argillic alteration and has many similarities to that of metamorphosed high-sulfidation systems and particularly a class of Au-rich VMS characterized by aluminous alteration. The LaRonde Penna and Bousquet 2-Dumagami deposits are interpreted to represent one large hydrothermal system in which variable contributions of hydrothermally modified seawater and magmatic volatiles contributed to the different styles of alteration and mineralization. The study illustrates that diverse styles of Au-rich VMS can coexist within the same deposit. In terms of exploration, almost all sulfide lenses or hydrothermal alterations minerals are located at or near volcanic hiatuses within the Bousquet Formation. These hiatuses represent major exploration targets especially when located in the upper part of the Bousquet Formation. The aluminous alteration zones have accommodated most of the postore strain due to their ductility and are transformed into schists. Consequently, the alteration product coincides spatially with the deformation zones despite the lack of a genetic relationship. Quartz-and Mn-rich garnet-biotite assemblages and/or aluminous schists with anomalous gold and/or zinc in intermediate to felsic transitional to calc-alkaline volcanic or volcaniclastic rocks located underneath a sedimentary cover represent excellent targets for Au-rich VMS in metamorphosed terranes.

ＡＳＲ焼却灰からの浮選による重金属の回収

Every year in Japan, approximately 0.7-0.8 million tons of automobile shredder residue (ASR) are generated and most incinerated ASR is landfilled. Since the landfill capacity for industrial and domestic waste is limited, the recycling of ASR is becoming very important. The incinerated ASR contains relatively large amount of non ferrous metals. Neverthless, only a small amount of these metals is recycled, pointing out the need to increase the recycling rate of these metals in order to save resources and reduce the amount of materials to be discarded. In this study, upgrading Cu and Zn from the incinerated ASR ash by means of flotation is described. In order to obtain the optimal condition, the effects of pH, grinding and the addition of reagents were investigated. As a result, it was found that grinding ash to c.a. 10 μm is necessary in order to obtain the optimum grade and recovery of Cu and Zn. Under the optimal conditions (i.e. pH 5; NaHS concentration of 21 kg/t; PAX concentration of 9 kg/t), Cu was upgraded from 3.2wt% to 8.7wt% recovering 49% of Cu. Moreover, Zn was upgraded from 1.4wt% to 2.8wt% recovering 36% of Zn. Cl content in both froth and tailings, on the other hand, was efficiently reduced from 3.3wt% to about 0.1wt%.

Zn-Pb-Cu VHMS deposits — extending the brine-pool pool

The massive sulphide deposits of the Devonian-Carboniferous Iberian pyrite belt (IPB) and the Ordovician Bathurst mining camp (BMC) have much in common: relative to others of this group like those of the Hokuroku basin they are large; have high aspect ratios; low Zn, Pb and Cu grades; high Fe/Cu, Zn/Cu and Pb/Zn ratios; high Sn; low fO2 mineral assemblages; evidence of Ba but scarcity of barite; ill-defined or no zone refining; and abundance of framboidal pyrite, mineral banding (bedding) and syn-depositional breccias. Differences include the vent complexes above stockwork pipes in the BMC, and biogenic S (negative d34S) in the IPB. There is evidence of sea-floor deposition, and fluid inclusion data from stockwork quartz in eight IPB deposits predict that the ore-forming fluids reversed buoyancy on mixing with seawater and ponded, sulphides precipitating immediately in the quenched ore-forming fluids. This manner of deposition explains many of the above ore characteristics while the biogenic S may be due to biostatic evolution. There is no reliable fluid inclusion evidence for the BMC but we suggest that the high degree of commonality between the camps points to brine-pool deposition for the BMC ore deposits. A previously proposed model involving buoyant fluids emerging into anoxic ocean water is vitiated by the evidence that host shales were deposited in oxic ocean water during mineralisation, and the lack of evidence for chimneys and rubble mounds that would be predicted by this hypothesis.

Typing Mineral Deposits Using Their Grades and Tonnages in an Artificial Neural Network

A test of the ability of a probabilistic neural network to classify deposits into types on the basis of deposit tonnage and average Cu, Mo, Ag, Au, Zn, and Pb grades is conducted. The purpose is to examine whether this type of system might serve as a basis for integrating geoscience information available in large mineral databases to classify sites by deposit type. Benefits of proper classification of many sites in large regions are relatively rapid identification of terranes permissive for deposit types and recognition of specific sites perhaps worthy of exploring further. Total tonnages and average grades of 1,137 well-explored deposits identified in published grade and tonnage models representing 13 deposit types were used to train and test the network. Tonnages were transformed by logarithms and grades by square roots to reduce effects of skewness. All values were scaled by subtracting the variable's mean and dividing by its standard deviation. Half of the deposits were selected randomly to be used in training the probabilistic neural network and the other half were used for independent testing. Tests were performed with a probabilistic neural network employing a Gaussian kernel and separate sigma weights for each class (type) and each variable (grade or tonnage). Deposit types were selected to challenge the neural network. For many types, tonnages or average grades are significantly different from other types, but individual deposits may plot in the grade and tonnage space of more than one type. Porphyry Cu, porphyry Cu-Au, and porphyry Cu-Mo types have similar tonnages and relatively small differences in grades. Redbed Cu deposits typically have tonnages that could be confused with porphyry Cu deposits, also contain Cu and, in some situations, Ag. Cyprus and kuroko massive sulfide types have about the same tonnages. Cu, Zn, Ag, and Au grades. Polymetallic vein, sedimentary exhalative Zn-Pb, and Zn-Pb skarn types contain many of the same metals. Sediment-hosted Au, Comstock Au-Ag, and low-sulfide Au-quartz vein types are principally Au deposits with differing amounts of Ag. Given the intent to test the neural network under the most difficult conditions, an overall 75% agreement between the experts and the neural network is considered excellent. Among the largestclassification errors are skarn Zn-Pb and Cyprus massive sulfide deposits classed by the neuralnetwork as kuroko massive sulfides—24 and 63% error respectively. Other large errors are the classification of 92% of porphyry Cu-Mo as porphyry Cu deposits. Most of the larger classification errors involve 25 or fewer training deposits, suggesting that some errors might be the result of small sample size. About 91% of the gold deposit types were classed properly and 98% of porphyry Cu deposits were classes as some type of porphyry Cu deposit. An experienced economic geologist would not make many of the classification errors that were made by the neural network because the geologic settings of deposits would be used to reduce errors. In a separate test, the probabilistic neural network correctly classed 93% of 336 deposits in eight deposit types when trained with presence or absence of 58 minerals and six generalized rock types. The overall success rate of the probabilistic neural network when trained on tonnage and average grades would probably be more than 90% with additional information on the presence of a few rock types.

Effect of impurity content on boundary sliding behavior in the superplastic Zn–22% Al alloy

A detailed investigation was conducted on the superplastic Zn–22% Al alloy to study the effect of impurity content on grain boundary sliding behavior in region I (low strain rate region), and region II (intermediate strain rate region, or the superplastic region) of the sigmoidal plot between stress and strain rate that was previously reported for the alloy. In conducting the investigation, three grades of Zn–22% Al were used; grades 1 and 2 contain 180 and 100 p.p.m. of impurities, respectively, whereas grade 3 is a high-purity grade containing 6 p.p.m. of impurities. The experimental results show that at intermediate strain rates (region II), the sliding behavior of the three grades of Zn–22% Al is similar and that the contribution of boundary sliding to the total strain, ξ, is about 60%. By contrast, the experimental data reveal that at low strain rates, the three grades exhibit significant differences regarding the sliding contribution. These differences are manifested in the following observations: (i) ξ in grade 3 at low strain rates is essentially equal to that at intermediate strain rates (region II), (ii) ξ in grade 1 or grade 2 is considerably lower than that at intermediate strain rates, and (iii) for the same low strain rate, ξ in grade 2 is higher than that in grade 1. The above observations regarding the effect of impurity level on boundary sliding behavior in Zn–22% Al are consistent with the concept of the interpretation of superplastic flow at low strain rates (low stresses) in terms of boundary segregation.

Application of Kalman learning algorithm multilayer neural network to estimates of ore grades

We have estimated lead (Pb) and zinc (Zn) grades along boreholes in an ore body based on geophysical logging data by using a Kalman learning algorithm, which is a variety of a back propagation neural network. The data set is from a Swedish mine, the Zinkgruvan Mine. It includes data from seven boreholes. Data on three geophysical logging parameters, gamma-ray, density and susceptibility, and the corresponding Pb and Zn grades obtained from chemical analysis of core samples were available from each borehole. Five of the boreholes were used for training the network and two boreholes were used for testing the successfulness in employing the network results for predictions of Pb and Zn grades. The principal idea of the Kalman learning algorithm is discussed. The minimum error rates of the Pb and Zn grades in the test set are 0.060 and 0.095, respectively. Their corresponding average prediction errors between predicted values from the network and the observed values obtained from the chemical analysis of core samples (expressed as a percentage) are 21.2 and 27.1 %, respectively. The optimum configuration of the neural network is a 4-layer neural network with 3 neurons in the input layer, 7 neurons in the first hidden layer, 3 neurons in the second hidden layer, and 1 neuron in the output layer. The optimum numbers of training epochs for Pb and Zn grades are 600 and 1400, respectively. The results obtained from applications of the Kalman learning algorithm to estimates of Pb and Zn grades in the test set are highly promising. A comparison with results from a conventional back propagation neural network shows that the results obtained from the Kalman learning algorithm are much better. Hence, the Kalman learning algorithm is demonstrated to be more effective than the conventional back propagation algorithm in predicting the ore grades.