Albite ± Actinolite-Altered Porphyry Dykes in Archean Gold Deposits of the Boulder Lefroy-Golden Mile Fault System, Yilgarn Craton, Western Australia: Petrography, Chronology, and Comparison to Canadian Albitites

The Boulder Lefroy-Golden Mile fault system in the Archean Yigarn Craton is the most productive gold-mineralized structure in Australia (>2300 t Au). The New Celebration deposit (51 t Au) is part of a group of hematite- and anhydrite-bearing mesothermal deposits and Fe-Cu-Au skarns associated with monzodiorite-tonalite intrusions in the strike-slip fault system. Ore-grade biotite-carbonate and late sericite-carbonate-alkali feldspar replacement is bound to the contacts of a felsic (low Cr, Ni, V) quartz-plagioclase porphyry dyke dated at 2676 ± 7 Ma. The sodic-potassic alteration of the felsic boudinaged dyke contrasts with the albite-actinolite alteration in the adjacent mafic (high Cr, Ni, V) plagioclase porphyry dated at 2662 ± 4 Ma, although both share the same sulfide-oxide assemblage: pyrite ± chalcopyrite, magnetite ± hematite. The younger porphyry locally crosscuts foliation and is bordered by post-kinematic actinolite-pyrite selvages overprinting talc-chlorite-phlogopite-dolomite schist. It contains auriferous pyrite (70 ppb Au; 610 ppb Ag) where sampled for zircon U-Pb chronology at +224 m elevation. Above the sample site, the dyke was mined as gold ore (1–6 g/t Au) at +300–350 m. Temperature estimates based on actinolite-albite pairs (300–350 °C) agree with the fluid inclusion trapping temperature of main-stage auriferous veins (330 ± 20 °C). These relationships are interpreted to indicate syn-mineralization emplacement. Gold-related albite-altered porphyry dykes (albitites) also occur in the world-class Hollinger-McIntyre (986 t Au) and Kerr Addison-Chesterville deposits (336 t Au), Abitibi greenstone belt, Canada.

Placemaking and visitors’ reviews of the Golden Mile of Durban

Orientation: Placemaking is a proclivity of cities to change space into place through zoning, naming and development into attractive, people-friendly landscapes where diverse, harmonious and sometimes contradicting amenities are coalesced to attract people.Research purpose: To establish the perceptions of the visitors on appeal, experience and safety of the Golden Mile of Durban.Motivation for the study: The study was motivated by availability of online reviews that remained unanalysed and did not aid decision-making.Research design, approach and method: Data were collected from 287 reviews sampled from the Golden Mile website. Qualitative analysis was performed on the data and categorised according to appeal, experience and safety associated with the Golden Mile.Main findings: The study found that placemaking is always work in progress as destinations strive for competitiveness and to avoid obsoletion. An overwhelming majority of visitors rated the Golden Mile as good to excellent on appeal, experience and safety. Some criticised the place as unsafe with a number of dilapidated buildings spoiling its appeal.Practical/managerial implications: Planners and tourism developers should factor the grass root approach to placemaking by increasing security and urging property owners to revamp their buildings, thus keeping with the image of the place.Contribution/value-add: The article emphasises the significance and value added by online visitors’ reviews in placemaking.

Invisible Gold Paragenesis and Geochemistry in Pyrite from Orogenic and Sediment-Hosted Gold Deposits

LA-ICPMS analysis of pyrite in ten gold deposits is used to determine the precise siting of invisible gold within pyrite, and thus the timing of gold introduction relative to the growth of pyrite and related orogenic events. A spectrum of invisible gold relationships in pyrite has been observed which suggests that, relative to orogenic pyrite growth, gold introduction in some deposits is early at the start of pyrite growth; in other deposits, it is late toward the end of pyrite growth and in a third case, it may be introduced at the intermediate stage of orogenic pyrite growth. In addition, we report a distinct chemical association of invisible gold in pyrite in the deposits studied. For example, in the Gold Quarry (Carlin type), Mt Olympus, Macraes and Konkera, the invisible gold is principally related to the arsenic content of pyrite. In contrast, in Kumtor and Geita Hill, the invisible gold is principally related to the tellurium content of pyrite. Other deposits (Golden Mile, Bendigo, Spanish Mountain, Witwatersrand Carbon Leader Reef (CLR)) exhibit both the Au-As and Au-Te association in pyrite. Some deposits of the Au-As association have late orogenic Au-As-rich rims on pyrite, which substantially increase the value of the ore. In contrast, deposits of the Au-Te association are not known to have Au-rich rims on pyrite but contain nano- to micro-inclusions of Au-Ag-(Pb-Bi) tellurides.

Chapter 12: Geologic Setting and Gold Mineralization of the Kalgoorlie Gold Camp, Yilgarn Craton, Western Australia

The Kalgoorlie gold camp in the Yilgarn craton of Western Australia comprises the supergiant Golden Mile and the smaller Mt. Charlotte, Mt. Percy, and Hidden Secret deposits. Since the camp’s discovery in 1893, ~1,950 metric tons (t) of Au have been produced from a total estimated endowment of ~2,300 t. The camp is located within Neoarchean rocks of the Kalgoorlie terrane, within the Eastern Goldfields superterrane of the eastern Yilgarn craton. Gold mineralization is distributed along an 8- × 2-km, NNW-trending corridor, which corresponds to the Boulder Lefroy-Golden Mile fault system. The host stratigraphic sequence, dated at ca. 2710 to 2660 Ma, comprises lower ultramafic and mafic lava flow rocks, and upper felsic to intermediate volcaniclastic, epiclastic, and lava flow rocks intruded by highly differentiated dolerite sills such as the ca. 2685 Ma Golden Mile Dolerite. Multiple sets of NNW-trending, steeply dipping porphyry dikes intruded this sequence from ca. 2675 to 2640 Ma. From ca. 2685 to 2640 Ma, rocks of the Kalgoorlie gold camp were subjected to multiple deformation increments and metamorphism. Early D1 deformation from ca. 2685 to 2675 Ma generated the Golden Mile fault and F1 folds. Prolonged sinistral transpression from ca. 2675 to 2655 Ma produced overprinting, NNW-trending sets of D2-D3 folds and faults. The last deformation stage (D4; < ca. 2650 Ma) is recorded by N- to NNE-trending, dextral faults which offset earlier structures. The main mineralization type in the Golden Mile comprises Fimiston lodes: steeply dipping, WNW- to NNW-striking, gold- and telluride-bearing carbonate-quartz veins with banded, colloform, and crustiform textures surrounded by sericite-carbonate-quartz-pyrite-telluride alteration zones. These lodes were emplaced during the earlier stages of regional sinistral transpression (D2) as Riedel shear-type structures. During a later stage of regional sinistral transpression (D3), exceptionally high grade Oroya-type mineralization developed as shallowly plunging ore shoots with “Green Leader” quartz-sericite-carbonate-pyrite-telluride alteration typified by vanadium-bearing muscovite. In the Hidden Secret orebody, ~3 km north-northwest of the Golden Mile, lode mineralization is a silver-rich variety characterized by increased abundance of hessite and petzite and decreased abundance of calaverite. At the adjacent Mt. Charlotte deposit, the gold-, silver-, and telluride-bearing lodes become subordinate to the Mt. Charlotte-type stockwork veins. The stockwork veins occur as planar, 2- to 50-cm thick, auriferous quartz-carbonate-sulfide veins that define steeply NW- to SE-dipping and shallowly N-dipping sets broadly coeval with D4 deformation. Despite extensive research, there is no consensus on critical features of ore formation in the camp. Models suggest either (1) distinct periods of mineralization over a protracted, ca. 2.68 to 2.64 Ga orogenic history; or (2) broadly synchronous formation of the different types of mineralization at ca. 2.64 Ga. The nature of fluids, metal sources, and mineralizing processes remain debated, with both metamorphic and magmatic models proposed. There is strong evidence for multiple gold mineralization events over the course of the ca. 2.68 to 2.64 orogenic window, differing in genesis and contributions from either magmatic or metamorphic ore-forming processes. However, reconciling these models with field relationships and available geochemical and geochronological constraints remains difficult and is the subject of ongoing research.