Gold occurrence in the footwall of the Lappberget Deposit, Garpenberg Mine, Sweden: Implications for recovery efficiency

• By-product metals have a significant potential to bring additional economic benefits to mines. However, a detailed characterization of their distribution is generally required to fulfill this potential and should preferably be integrated into a geometallurgical assessment. This contribution presents a detailed mineralogical and textural investigation of gold-bearing phases at the footwall of the Zn–Pb–Ag–(Cu–Au) Lappberget Deposit, Garpenberg Mine, Sweden, using optical microscopy, scanning electron microscope with energy dispersive spectroscopy (SEM-EDS), electron probe microanalysis (EPMA), laser ablation-inductively coupled plasma mass spectrometer (LA-ICPMS), and bulk chemical analysis applied to drill core and Knelson concentrator samples. Gold is a by-product at the Garpenberg mine, but it is unclear how the mineralogy, occurrence, and distribution of gold-bearing phases impact on gold recoveries during mineral processing. Our results show that Au-dominant electrum is the most abundant gold-bearing phase in the footwall of the Lappberget deposit, occurring strongly associated to sulfides in a variety of textures and grain sizes. Electrum grains commonly occur within sulfide borders, as inclusions, intergrowth and overgrowths of chalcopyrite, pyrite, galena, sphalerite, and pyrrhotite. Gangue minerals may also contain disseminated electrum and inclusions. Electrum grain sizes range from ∼5 µm to 300 µm, predominantly below 100 µm. The potential of sulfide lattice-bound invisible gold in the form of solid-solution gold and colloidal gold was also investigated, showing Au depletion within the analyzed sulfide carriers. The analysis of the concentrate samples from the Knelson gravity concentrator showed 584 and 431 ppm of gold content. High degree of liberation is observed among the gold-bearing phases in the concentrate, and gold recovery is highest among fractions coarser than 106 µm mesh. Pyrite and galena are the most abundant minerals in the concentrate samples. The gold-bearing phases were categorized based on its mineralogy, texture, grain size, and association and their influence on gold processing, especially textures and grain size, which implicates its liberation in milling and recovery by the gravity separator.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Multidisciplinär geovetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geosciences, Multidisciplinary (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Metallurgi och metalliska material (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Metallurgy and Metallic Materials (hsv//eng)

Nyckelord

Gold characterization

Gold as a by-product

Geometallurgy of gold

Lappberget ore

Garpenberg Mine

Ore Geology

Malmgeologi

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