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Annex C3 – Geology and Geochemistry Supplemental Information C3 - 2 DISCUSSION OF GOLD MINERALISATION PROCESSES Gold is principally associated with belts of Proterozoic Birimian and Tarkwaian rocks. The bulk of the gold, about 80 percent, comes from primary lode occurrences within Birimian rocks (Figure 3-5), which together with their associated intrusives, occur over approximately one third of the country (Wright and Hastings 1985). The remainder of the gold produced comes mainly from the blanket conglomerate deposits (possible paleo placers) of the Tarkwaian System and from placer mines exploiting material derived from both the Birimian and Tarkwaian source rocks. The Birimian Gold Belts are a set of six parallel, evenly spaced, northeast trending volcanic ridges over 300 km long (see for example the Ashanti Belt, Figure 3-5). Steeply dipping, regional shears bound these ridges, which are separated by basins containing metamorphosed pyroclastic and metasedimentary rocks (Figure 3-5). Within the Birimian, primary gold is associated with a typical submarine exhalative volcanosedimentary facies developed along narrow laterally continuous zones at the boundary between volcanic belts and the sedimentary basins. This primary, syn-sedimentary gold was subjected to migration and concentration in northeast trending regional shear zones during metamorphism and the emplacement of the Birimian intrusives, as well as during major structural events. LOCAL GEOLOGIC SETTING DISCUSSION The Akyem deposit is localized in the hanging wall (upper side or plate) of a regional fault that trends to the northeast (N70 o E) parallel to regional structures, and dips about 60 degrees to the southeast (Figures 3-6 and 3-7), parallel to the foliation developed in the Birimian host rock. The planar fault structure (thrust fault) (Feybesse 1999; Lescuyer 1999) is intensely sheared and exhibits a mylonitic to cataclastic fragmental texture consisting of lens of metavolcanic fragments in a matrix of sheared and plastically deformed graphitic material. The presence of graphitic rubble zones suggests reactivation of the fault zone over time. The fault occurs in fine-grained, gray-green massive to locally sheared Birimian mafic metavolcanic rocks exhibiting chlorite and carbonate alteration that locally contain euhedral magnetite. Immediately overlying the metavolcanics is a distinctive gray-green-pink unit containing blue quartz phenocrysts in a mylonitic matrix (quartz epiclastic rock). The upper and lower contacts of this unit are typically sheared and brecciated and the upper contact of this unit is locally in sharp contact withoverlying light gray-tan chert (Monthel et al. 2001). This unit is considered sedimentary and represents a distinctive marker between the metavolcanic and metasedimentary units of the Birimian. The overlying metasedimentary rocks are for the most part turbidite sequences consisting of greywacke, argillites, black carbonaceous siltstone, and fine-grained arkosic sandstones. This unit grades upwards into a saprolitically weathered zone (deeply weathered bedrock largely altered to clay) that ranges from 10 to 50 meters thick. The saprolite consists of lateritic clay and quartz fragments with as much as 25 percent weathered rock remaining within the saprolite. Near the surface, in the upper 1 to 5 meters, red lateritic clay is developed as subsoil. Akyem Gold <strong>Mining</strong> Project November 2008 FINAL EIS
Annex C3 – Geology and Geochemistry Supplemental Information C3 - 3 MINERALISATION DISCUSSION The Akyem deposit is localized along a southeast dipping, graphite-bearing, mylonitic fault zone that ranges from 1 to 15 meters thick. Mineralisation is present almost exclusively in the hanging wall, with the fault structure defining a sharp base to the mineralisation of the deposit (Figure 3-7). Ore above the fault ranges in thickness from 10 to 100 meters and is developed in two principal shoots, both of which plunge to the southeast parallel to the fault. Associated, sub parallel structures have created dilation zones in rocks of the upper plate that have enhanced the development of mineralisation. The deposit is developed over approximately 2,500 meters in strike length (along the fault) and ore has been delineated to a depth of about 400 meters down the southeast dipping fault structure. Based on this delineation drilling, ore grade mineralisation likely continues at depth below the zone of current exploration. Mineralisation thins both to the northeast and southwest along the strike of the localizing fault structure. Gold is hosted in each of the three units described above including the lower mafic volcanic, quartz epiclastic, and the upper greywacke units. Ore grades follow alteration patterns with the most intense alteration and highest gold grades occurring nearest the fault zone and in general decreasing away from the zone. Gold typically occurs as fine-grained disseminations in moderate to intense hydrothermally altered, metamorphic volcanic and sedimentary host rocks. Locally some visible gold is present. ALTERATION AND MINERALOGY DISCUSSION Alteration is largely restricted to hanging wall rocks with the assemblages most intimately associated with higher-grade gold mineralisation containing abundant quartz (silica flooding and veining), extensive patchy appearing iron and calcium carbonate replacements, and minor pyrite. Three patterns of alteration assemblages, mineral zonation and gold grades are recognized at Akyem and are briefly described in Table C3-1 from more distal assemblages (chlorite, sericite and green mica) to more proximal assemblages (quartz, ironcarbonate, pyrite). TABLE C3-1 Alteration Assemblages, Zonation and Gold Grades Grade Stage Mineralogy Comment g/t Gold Alteration 1 Weak Alteration 2 Moderate Alteration 3 Intense Calcite-Chlorite 0-0.6 Iron-Carbonate Chlorite Sericite Pyrite Magnetite Quartz Iron-Carbonate Sericite Pyrite Note: g/t = grams per ton 0.6-3.0 (avg. 2.0) > 3.0 Weak alteration; carbonate and clay alteration on the margins of ore deposit; best developed in mafic volcanics and sediments. Low gold grade. Moderate alteration; iron dolomite and ankerite with chlorite, calcite and pyrite (0-3%, avg.
Page 1 and 2: A N N E X C SUPLEMENTAL INFORMATION
Page 3 and 4: Annex C1 - Flora and Fauna Species
Page 23 and 24: ANNEX C-2 AQUATIC RESOURCES SUPPLEM
Page 25 and 26: Annex C2 - Aquatic Resources Supple
Page 27 and 28: Annex C2 - Aquatic Resources Supple
Page 29: Annex C3 - Geology and Geochemistry
Page 33 and 34: Annex C3 - Geology and Geochemistry
Page 35 and 36: Drill Hole ID Core Interval (meters
Page 41 and 42: TABLE C3-5 (continued) Lithology Ke
Page 45 and 46: TABLE C3-7 Results of Synthetic Pre
Page 47 and 48: TABLE C3-7 (continued) Results of S
Page 49 and 50: TABLE C3-8 Results of Biological Ac
Page 51 and 52: TABLE C3-8 (continued) Results of B
Page 53 and 54: TABLE C3-9 (continued) Results of P
Page 55 and 56: TABLE C3-9 (continued) Results of P
Page 57 and 58: Annex C4 - Water Resources Suppleme
Page 59 and 60: Flow (m3/sec) 80 70 60 50 40 30 20
Page 63 and 64: Flow (m3/sec) 80 70 60 50 40 30 20
Page 67 and 68: Surface Water Statistic Afosu Strea
Page 73 and 74: Piper Diagram for Pra River and Tri
Page 75 and 76: Seep Water Statistic All Seep Sampl
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Annex C4 - Water Resources Suppleme
Page 83 and 84:
Groundwater Elevation (meters re ms
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Groundwater Elevation (meters re ms
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Annex C4 - Water Resources Suppleme
Page 89 and 90:
Table C4-7 Groundwater Chemistry (2
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Surface Water Statistic Village Wel
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Surface Water Statistic Village Wel
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Groundwater Type Statistic Village
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Piper Diagram for Village Wells Aky
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Annex C5 - Soil Resources Supplemen
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Series BEKWAI NZIMA KOKOFU ODA TEMA
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Annex C6 -- Noise Supplemental Info
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Annex C6 -- Noise Supplemental Info
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ANNEX C-7 SOCIOECONOMICS SUPPLEMENT
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Annex C7 -- Socioeconomics Suppleme
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