MAPPING THE MINERAL ZONATION AT THE ERNEST HENRY IRON OXIDE COPPER-GOLD DEPOSIT: VECTORING TO Cu-Au MINERALIZATION USING MODAL MINERALOGY

Iron oxide copper-gold (IOCG) deposits form in spatial and genetic relation to hydrothermal iron oxide-alkali-calcic-hydrolytic alteration and thus show a mappable zonation of mineral assemblages toward the orebody. The mineral zonation of a breccia matrix-hosted orebody is efficiently mapped by regularly spaced samples analyzed by the scanning electron microscopy-integrated mineral analyzer technique. The method results in quantitative estimates of the mineralogy and allows the reliable recognition of characteristic alteration as well as mineralization-related mineral assemblages from detailed mineral maps. The Ernest Henry deposit is located in the Cloncurry district of Queensland and is one of Australia’s significant IOCG deposits. It is known for its association of K-feldspar altered clasts with iron oxides and chalcopyrite in the breccia matrix. Our mineral mapping approach shows that the hydrothermal alteration resulted in a characteristic zonation of minerals radiating outward from the pipe-shaped orebody. The mineral zonation is the result of a sequence of sodic alteration followed by potassic alteration, brecciation, and, finally, by hydrolytic (acid) alteration. The hydrolytic alteration primarily affected the breccia matrix and was related to economic mineralization. Alteration halos of individual minerals such as pyrite and apatite extend dozens to hundreds of meters beyond the limits of the orebody into the host rocks. Likewise, the Fe-Mg ratio in hydrothermal chlorites changes systematically with respect to their distance from the orebody. Geochemical data obtained from portable X-ray fluorescence (p-XRF) and petrophysical data acquired from a magnetic susceptibility meter and a gamma-ray spectrometer support the mineralogical data and help to accurately identify mineral halos in rocks surrounding the ore zone. Specifically, the combination of mineralogical data with multielement data such as P, Mn, As, P, and U obtained from p-XRF and positive U anomalies from radiometric measurements has potential to direct an exploration program toward higher Cu-Au grades.

Fluid Inclusion Study of Epithermal Quartz Veins from the Kyaukmyet Prospect, Monywa Copper-Gold Ore Field, Central Myanmar

The Kyaukmyet prospect is located near the main ore bodies of the Kyisintaung and Sabetaung high-sulfidation Cu-Au deposits, Monywa copper-gold ore field, central Myanmar. Lithologic units in the research area are of mainly rhyolite lava, lapilli tuff and silicified sandstone, mudstone and siltstone units of Magyigon Formation which hosted to be polymetallic mineralization. Our field study recorded that epithermal quartz veins are hosted largely in rhyolite lava and lapilli tuff units. Those quartz veins show crustiform, banded (colloform), lattice bladed texture and comb quartz. The main objectives of the present research in which fluid inclusion studies were considered to conduct the nature, characteristics and hydrothermal fluids evolution from the epithermal quartz veins. In this research, there are three main types of fluid inclusions are classified according to their phase relationship (1) two-phase liquid-rich inclusions, (2) the coexisting liquid-rich and vapor-rich inclusions, and (3) only vapor-rich inclusions. Microthermometric measurements of fluid inclusions yielded homogenization temperatures (Th) of 148–282 °C and final ice-melting temperature (Tm) of -0.2°C to -1.4°C . The value of (Tm) are equal to the salinities reaching up 0.35 to 2.07 wt % NaCl equiv. respectively. Estimation formation temperature of the quartz veins provide 190°C and 210°C and paleo-depth of formation are estimated to be between 130m and 210m. Petrography of fluid inclusion and microthermometric data suggest that fluid boiling as well as mixing processes were likely to be happened during the hydrothermal fluid evolution at the Kyaukmyet prospect. According to the characteristics of many parameters including petrography of fluid inclusion, microthermometric data, paleo-depth, evidence of quartz vein textures and types of hydrothermal alteration from the Kyaukmyet prospect allows to interpret these data to be the low-sulfidation epithermal system.

Geochemical Compositions and Detrital Minerals of Stream Sediments around the Zijinshan Copper-Gold Orefield and Their Implications

Regional geochemical anomalies in stream sediments often have close spatial relationships with metallogenic provinces or ore districts, but the relationships between them have not been examined in depth. In this study, stream sediments were collected around the Zijinshan Copper-Gold Orefield, Fujian Province, China. Element geochemistry, U–Pb geochronology and Hf isotope compositions of detrital zircons, and electron microprobe and LA-ICP-MS analyses of iron oxides were conducted. The aims of this study were to investigate the relationship between the provenance of the stream sediments and ore-bearing magmatic rocks in the Zijinshan Copper-Gold Orefield, and to explore the enrichment mechanism of the ore-forming elements in stream sediments. The results show that the ore-forming elements and their associated elements are most significantly enriched in stream sediments near the orefield. U–Pb ages and Hf isotopic compositions of detrital zircons in the sediments closest to the orefield carry information on the ore- bearing magmatic rocks in the orefield. However, as the stream sediments are relatively far from the orefield, the degree of enrichment of ore-forming elements and the detrital zircon U–Pb age signals of the ore-bearing magmatic rocks in the orefield rapidly weaken. This weakening of the geochemical signals may have been affected by many factors, such as lithological resistance to weathering, vegetation coverage, micro-topographic conditions, etc. In-situ elements analysis of iron oxides and elemental correlation analysis of stream sediments indicate iron oxides and clay minerals are the main carrier minerals for the migration of ore-forming elements.

Determination of Abrasiveness in Copper-Gold Sulfide Ores: A Contribution to the Geometallurgical Model of the Sossego Deposit

The geological context of this study is established in the iron oxide-copper-gold (IOCG) deposit of Sossego (Canaã dos Carajás, Brazil), where hydrothermal alterations in shear zones concentrated the metals of interest and added new characteristics to the metavolcanic-sedimentary and granite rocks. The mineral transformation of rocks by hypersaline fluids enriched in metals and silica also modifies some metallurgical properties, such as abrasiveness. Special bench tests on rock drill cores are used in mapping the abrasiveness of rocks, with the Bond abrasion test being more commonly used in the mining industry, but it has a restrictive sampling protocol and mass requirement for geometallurgical studies. As a counterpoint, the test of the Laboratoire Central des Ponts et Chaussées/Central Laboratory of Bridges and Roads (LCPC) requires a smaller amount of fine material and a finer granulometric range. The study on the use of LCPC was implemented in 40 samples, using Bond Ai as a reference. The results showed a strong correlation between both methodologies (R2 = 95%), validating the use of LCPC to quantify abrasiveness in the Sossego mine. It was also possible to classify the most abrasive lithologies.

ANALISIS PENENTUAN SAHAM PORTOFOLIO OPTIMAL DENGAN MODEL MARKOWITZ PADA PERUSAHAAN SEKTOR PERTAMBANGAN YANG TERDAFTAR DI BURSA EFEK INDONESIA PERIODE JANUARI 2019 – DESEMBER 2020

Dalam kegiatan investasinya, pasar modal menawarkan berbagai pilihan berinvestasi dengan tingkat keuntungan (return) dan tingkat risiko (risk) yang berbeda-beda. Untuk mengurangi risiko dalam investasi tersebut maka investor membentuk sebuah portofolio. Portofolio optimal dengan model Markowitz yang dipilih dari sekian banyak alternatif portofolio efisien dapat memberikan tingkat return yang maksimal sesuai dengan risiko yang berani ditanggung oleh investor. Tujuan penelitian ini untuk mengetahui portofolio saham yang optimal serta proporsi dana masing-masing saham dengan menggunakan model Markowitz. Penelitian dilakukan di BEI pada saham perusahaan sektor pertambangan periode Januari 2019-Desember 2020. Data yang digunakan dalam penelitian adalah data sekunder yang diperoleh dari www.idx.co.id dan www.finance.yahoo.com. Jumlah populasi dalam penelitian ini adalah 47 saham perusahaan sector pertambangan yang terdaftar di Bursa Efek Indonesia periode Januari 2019-Desember 2020 dan jumlah sampel sebanyak 11 saham perusahaan, dengan teknik purposive sampling. Hasil penelitian ini menunjukkan bahwa dari 11 saham perusahaan diperoleh sebanyak 4 saham yang masuk dalam portofolio optimal menggunakan model Markowitz dengan jumlah proporsi dananya yakni PT. Harum Energy Tbk (HRUM) sebesar 12,45%, PT. Timah Tbk (TINS) sebesar 24,42%, PT. Merdeka Copper Gold Tbk (MDKA) sebesar 53,07% dan yang terakhir PT. Indika Energy Tbk (INDY) sebesar 10,05%. Memberikan expected return sebesar 4,70% dan tingkat risiko sebesar 2,83%.

Chemistry of chlorite from the K-silicate-sericitic alteration in Elatsite porphyry Cu-Au deposit, Bulgaria

The K-silicate-sericitic alteration is one of the well-preserved hydrothermal alterations at the Elatsite porphyry-copper gold deposit (PCGD). It is observed in all lithological varieties, but shows asymmetric distribution of the secondary products. The alteration is genetically related with the occurrence of the K-silicate and Na-Ca-K-silicate alteration. The K-silicate-sericitic alteration has simple mineral content which includes mainly chlorite and sericite. The temperature of formation of the alteration is estimated between 250–268 °C.

Structural Evolution of the Central Kiruna Area, Northern Norrbotten, Sweden: Implications on the Geologic Setting Generating Iron Oxide-Apatite and Epigenetic Iron and Copper Sulfides

To guide future exploration, this predominantly field based study has investigated the structural evolution of the central Kiruna area, the type locality for iron oxide-apatite deposits that stands for a significant amount of the European iron ore production. Using a combination of geologic mapping focusing on structures and stratigraphy, petrography with focus on microstructures, X-ray computed tomography imaging of sulfide-structure relationships, and structural 2D-forward modeling, a structural framework is provided including spatial-temporal relationships between iron oxide-apatite emplacement, subeconomic Fe and Cu sulfide mineralization, and deformation. These relationships are important to constrain as a guidance for exploration in iron oxide-apatite and iron oxide copper-gold prospective terrains and may help to understand the genesis of these deposit types. Results suggest that the iron oxide-apatite deposits were emplaced in an intracontinental back-arc basin, and they formed precrustal shortening under shallow crustal conditions. Subsequent east-west crustal shortening under greenschist facies metamorphism inverted the basin along steep to moderately steep E-dipping structures, often subparallel with bedding and lithological contacts, with reverse, oblique to dip-slip, east-block-up sense of shears. Fe and Cu sulfides associated with Fe oxides are hosted by structures formed during the basin inversion and are spatially related to the iron oxide-apatite deposits but formed in fundamentally different structural settings and are separated in time. The inverted basin was gently refolded and later affected by hydraulic fracturing, which represent the last recorded deformation-hydrothermal events affecting the crustal architecture of central Kiruna.