Albert Fon - Academia.edu (original) (raw)

Papers by Albert Fon

SN applied sciences, Apr 18, 2023

Gold mineralization of the Upper Lom Basin in the eastern Cameroon goldfield is spatially associa... more Gold mineralization of the Upper Lom Basin in the eastern Cameroon goldfield is spatially associated with tourmaline. The goldfield belongs to the Adamawa-Yadé Domain of the Central African Fold Belt and is characterized by eluvial, alluvial and lode gold deposits of Pan-African age. This paper examines the chemistry and morphology of saprock gold and its link with tourmaline in the host rock. Tourmaline chemistry was obtained using the electron microprobe analysis (EMPA) technique while gold grains were examined for morphology and microchemistry using the EMPA equipped with scanning electron microscopy and energy dispersive spectrum instruments. The tourmaline compositional data plot in the dravite field, and belongs to the alkali group showing major element variations that are typical of tourmaline associated with granite-related orogenic gold deposits common along shear zones. Gold alloy composition (Ag, Cu) suggests multiple gold precipitation events due to episodic fluid influx, with a range of 572-1000 gold fineness. We infer that tourmaline development and gold deposition were coeval within the aureole around the pluton and involved reduced hydrothermal fluids with low salinity. The high δ 11 B in the tourmaline also points to fluid derivation from the Pan African granitic basement widely recognized to be fertile in gold in eastern Cameroon. Tourmaline textural-chemical features such as low Na content and gold microchemistry point to granite-related hydrothermal style of primary gold mineralization, and has implications for exploration as tourmaline-rich rocks in the vicinity of the felsic plutons in the Lom Basin would be optimal target areas for future exploration.

Geochemistry: Exploration, Environment, Analysis, 2018

Hydrothermally altered granitoids in the Batouri district host gold mineralization. Gold and asso... more Hydrothermally altered granitoids in the Batouri district host gold mineralization. Gold and associated metals occur as disseminated, stockwork and veins. The granitoids range from quartz-alkali granitoids sensu stricto to diorite with various types of wallrock alterations including K-feldspar alteration, sericitization, silicification, and sulphidation/ferruginization. Most gold-bearing samples are extensively brecciated. Gold mineralization is accompanied with sericitization, silicification, and sulphidation/ferruginization alterations. Gold concentrations reach a high of 103.7 ppm. The granitic rocks are sub-alkaline. They show enrichment in the LREE, a negative Eu anomaly and a depletion in the HREE reflecting the breakdown and mobility of the initial plagioclase feldspar bearing HREE during fluid-rock interaction. On multielement variation diagrams, spikes at K, Ba, Pb, and Th are depicted resulting from selective enrichment during alteration. Mass gains/losses during alteration calculated using the immobile element method indicate, amongst others, gains in SiO2 (silicification), K2O (K-feldspar alteration), SO3 and Fe2O3 (sulphidation/ferruginization) with losses in Na2O linked to sericitization. The samples show Pd and Pt as high as 2 ppm. Gold mineralization is associated with wallrock alteration zones with elevated contents of As-Ba-Cu-Pb-Rb-Sr-Zn and Zr due to the neominerals developed during hydrothermal alteration. Au-Ag-Zn defines a potential pathfinder element cluster in the Batouri district.

Journal of African Earth Sciences, 2015

Abstract The microchemical signature of alluvial gold particles has wide application in constrain... more Abstract The microchemical signature of alluvial gold particles has wide application in constraining their primary sources. In this study, we apply this concept to investigate the composition of gold-bearing alloys from alluvial samples draining two geologically distinct terrains in southern and eastern Cameroon where the search for primary gold has remained elusive. The first set of gold grains (Lom grains) are from the Lom river drainage system with predominantly metasedimentary Pan-African rocks in the catchment region while the second set of grains (Nyong grains) are from the Mbal and Ebap tributaries of the Nyong river draining over a Paleoproterozoic complex comprising metamorphosed ultramafic rocks, amphibolites and granulitic gneisses. The gold grains recovered from these fluvial networks after panning were first studied under an electron microscope in order to evaluate their morphological features and subsequently embedded in epoxy resin, polished, and their compositions determined by both electron microprobe (EMPA) and laser ablation (LA-ICP-MS) techniques. The Lom grains are irregular to sub rounded with extensively pitted surfaces while the Nyong grains are predominantly rounded, oblong and with smooth surfaces. Nyong grains are devoid of inclusions while galena and pyrite are entombed in the Lom grains. Both set of grains are essentially Au–Ag alloys although the Ag content of the cores of the Nyong grains from both EMPA and LA-ICP-MS analytical techniques are significantly lower (0.05–6.07 wt% Ag; 93.54–99.29 wt% Au) than for Lom gold (0.06–22.75 wt% Ag; 78.76–99.86 wt% Au). X-ray element distribution maps do not show any zonal variation in core composition suggesting the gold grains derived from lode sources with single episode of hydrothermal gold deposition. Also the Nyong grains have significant amounts of Pt, Pd and Cr suggesting a link with ultramafic rocks while the Lom grains have substantial Sb and Zn levels pointing to hydrothermal quartz veining as the possible primary mineralization system. The grains from both localities have Ag-depleted rims. The results demonstrate that the microchemical signature of gold is useful to study the hypogene environment of a given area and a field for hydrothermal-orogenic gold is proposed on the ternary Au–Ag–Hg and Au–Ag–Cu plots.

International Journal of Geosciences, 2014

Stream sediments are widely employed in reconnaissance exploration for gold especially in areas w... more Stream sediments are widely employed in reconnaissance exploration for gold especially in areas where outcrops are scarce and the overburden thick such as in the eastern Cameroon goldfields. In this study, 337 stream sediment samples were collected from the Lom river drainage basin. The study aims at identifying the main geological processes affecting the geochemical data from the sediments by considering the multi-elements relationships and spatial features of single elements. The samples were collected in duplicate. One set was panned, gold grains picked and weighed while the second set was wet sieved and the ≤100 microns size fraction retained. This fraction was eventually analyzed for gold by fire assay and a suite of elements by inductively coupled plasma mass spectrometry (ICP-MS). Single element maps were constructed using ArcGIS and the relationship between elements measured using Pearson correlation and principal component analysis (PCA). Gold concentrations in the samples are erratic, most below the detection limit and attain a high of 450 ppm. Five factors are derived from the PCA including single element factors for As and Au reflecting bedrock-hosted mineralization. The Cu-Zn-Y-Nb-Pb factor suggests sulphide mineralization perhaps related to felsic intrusions while the Sr-Ba-LaCe -Zr factor is linked to lithologic control. These results demonstrate the usefulness of multi-element analysis and data interpretation using GIS tools in the exploration efforts for gold worldwide.

Geochemistry

Abstract The distribution of gold in the weathering blanket at the Belikombone gold prospect in e... more Abstract The distribution of gold in the weathering blanket at the Belikombone gold prospect in east Cameroon provides insights into gold mobility in the secondary environment and in tropical terrains worldwide. Both gridline-controlled sampling of topsoil (surface samples) and sampling of various layers in pits are used and the gold assay for each sample determined by NiS fire assay with ICP-AES finish. One hundred and thirty-two (132) surface samples and a total of 206 samples from 19 exploration pits were analyzed. The results from the topsoil samples show an anomaly with the highest Au concentration at 5.9 mgkg-1. The mineralization corridor follows a NE-SW trend. The horizons within the pits range from sap rock at the base, through saprolite, rubble layer rich in relict quartz material to a ferruginous loose layer at the top although some horizons are missing in some pits. All the layers contain gold and the highest concentration in the sap rock horizon is 3.4 mgkg-1 while the rubble layer has a gold high of 6.1 mgkg-1. The individual soil horizons show no systematic gold trends and given the presence of gold in all layers, the patterns point towards supergene dissolution and redistribution of gold. Gold enrichment within the upper horizons in the weathering blanket is attributed to sequestration by Fe oxides of chemically remobilized gold. However, the high gold content within the sap rock and saprolite layers suggests that migration of gold in the particulate form supersedes chemical gold redistribution. Particulate gold obtained by panning samples from the pits varies in shape from euhedral, elongated to irregular. Electron microprobe analysis on the grains record high contents of gold in the rim zones (90.0 to 99.8 wt%). The cores are relatively rich in Ag (12.6 to 14.2 wt%) while the rims are poor in Ag. The low Ag content in the rims is attributed to the preferential leaching of Ag. The soil pH value in this area varies between 3.6 and 7.3. Under such acidic to near neutral conditions, bisulfide and thiosulfate ions can dissolve and transport Au and Ag to be precipitated under surficial conditions creating authigenic Au haloes especially in the saprolite and sap rock layers. Such pH values together with oxidizing Eh conditions explain the solubility of gold in the area. These results are important for geochemical exploration of gold in tropical terrains, and confirm previous studies.

The distribution of gold in the weathering blanket at the Belikombone gold prospect in east Camer... more The distribution of gold in the weathering blanket at the Belikombone gold prospect in east Cameroon provides insights into gold mobility in the secondary environment and in tropical terrains worldwide. Both gridline-controlled sampling of topsoil (surface samples) and sampling of various layers in pits are used and the gold assay for each sample determined by NiS fire assay with ICP-AES finish. One hundred and thirty-two (132) surface samples and a total of 206 samples from 19 exploration pits were analyzed. The results from the topsoil samples show an anomaly with the highest Au concentration at 5.9 mgkg-1. The mineralization corridor follows a NE-SW trend. The horizons within the pits range from sap rock at the base, through saprolite, rubble layer rich in relict quartz material to a ferruginous loose layer at the top although some horizons are missing in some pits. All the layers contain gold and the highest concentration in the sap rock horizon is 3.4 mgkg-1 while the rubble la...

International Journal of Geosciences, 2012

Exploration for primary gold in tropical settings is often problematic because of deep weathering... more Exploration for primary gold in tropical settings is often problematic because of deep weathering and the development of a thick soil cover. In this paper we present the results of both chargeability and resistivity surveys carried out over the Belikombone hill gold prospect (14˚00'-14˚25'E, 5˚25'-6˚00'N) in the Betare Oya area (eastern Cameroon), where previous soil sampling had identified gold anomalies. The geophysical data were obtained using Syscal Junior 48 resistivity meter and the Schlumberger configuration array for both the vertical electrical soundings (VES) and horizontal profiling. These data were further built into a GIS framework and the continuity of favourable gold-bearing structures at depth modeled using WINSEV, RED2INV and SURFER extensions softwares. IP (Induced Polarization)-chargeability and resistivity data combined, have identified irregular anomalous zones trending NE-SW. This trend is consistent with the attitude of most auriferous quartz veins exposed in artisanal pits and parallel to the regional shear zone system and foliations. The high resistivity anomalies correspond to quartz veins while the relatively high IP anomalies correspond to low sulphide ± gold concentrations in the quartz veins. Modeling IP-chargeability and resistivity data prepared as contours and 3D maps, culminated to the development of an inferred, irregular and discontinuous mineralized body at depths of up to 95 m. The size and shape of this mineralized body can only later be tested by drilling to ascertain the resource.

SN applied sciences, Apr 18, 2023

Gold mineralization of the Upper Lom Basin in the eastern Cameroon goldfield is spatially associa... more Gold mineralization of the Upper Lom Basin in the eastern Cameroon goldfield is spatially associated with tourmaline. The goldfield belongs to the Adamawa-Yadé Domain of the Central African Fold Belt and is characterized by eluvial, alluvial and lode gold deposits of Pan-African age. This paper examines the chemistry and morphology of saprock gold and its link with tourmaline in the host rock. Tourmaline chemistry was obtained using the electron microprobe analysis (EMPA) technique while gold grains were examined for morphology and microchemistry using the EMPA equipped with scanning electron microscopy and energy dispersive spectrum instruments. The tourmaline compositional data plot in the dravite field, and belongs to the alkali group showing major element variations that are typical of tourmaline associated with granite-related orogenic gold deposits common along shear zones. Gold alloy composition (Ag, Cu) suggests multiple gold precipitation events due to episodic fluid influx, with a range of 572-1000 gold fineness. We infer that tourmaline development and gold deposition were coeval within the aureole around the pluton and involved reduced hydrothermal fluids with low salinity. The high δ 11 B in the tourmaline also points to fluid derivation from the Pan African granitic basement widely recognized to be fertile in gold in eastern Cameroon. Tourmaline textural-chemical features such as low Na content and gold microchemistry point to granite-related hydrothermal style of primary gold mineralization, and has implications for exploration as tourmaline-rich rocks in the vicinity of the felsic plutons in the Lom Basin would be optimal target areas for future exploration.

Geochemistry: Exploration, Environment, Analysis, 2018

Hydrothermally altered granitoids in the Batouri district host gold mineralization. Gold and asso... more Hydrothermally altered granitoids in the Batouri district host gold mineralization. Gold and associated metals occur as disseminated, stockwork and veins. The granitoids range from quartz-alkali granitoids sensu stricto to diorite with various types of wallrock alterations including K-feldspar alteration, sericitization, silicification, and sulphidation/ferruginization. Most gold-bearing samples are extensively brecciated. Gold mineralization is accompanied with sericitization, silicification, and sulphidation/ferruginization alterations. Gold concentrations reach a high of 103.7 ppm. The granitic rocks are sub-alkaline. They show enrichment in the LREE, a negative Eu anomaly and a depletion in the HREE reflecting the breakdown and mobility of the initial plagioclase feldspar bearing HREE during fluid-rock interaction. On multielement variation diagrams, spikes at K, Ba, Pb, and Th are depicted resulting from selective enrichment during alteration. Mass gains/losses during alteration calculated using the immobile element method indicate, amongst others, gains in SiO2 (silicification), K2O (K-feldspar alteration), SO3 and Fe2O3 (sulphidation/ferruginization) with losses in Na2O linked to sericitization. The samples show Pd and Pt as high as 2 ppm. Gold mineralization is associated with wallrock alteration zones with elevated contents of As-Ba-Cu-Pb-Rb-Sr-Zn and Zr due to the neominerals developed during hydrothermal alteration. Au-Ag-Zn defines a potential pathfinder element cluster in the Batouri district.

Journal of African Earth Sciences, 2015

Abstract The microchemical signature of alluvial gold particles has wide application in constrain... more Abstract The microchemical signature of alluvial gold particles has wide application in constraining their primary sources. In this study, we apply this concept to investigate the composition of gold-bearing alloys from alluvial samples draining two geologically distinct terrains in southern and eastern Cameroon where the search for primary gold has remained elusive. The first set of gold grains (Lom grains) are from the Lom river drainage system with predominantly metasedimentary Pan-African rocks in the catchment region while the second set of grains (Nyong grains) are from the Mbal and Ebap tributaries of the Nyong river draining over a Paleoproterozoic complex comprising metamorphosed ultramafic rocks, amphibolites and granulitic gneisses. The gold grains recovered from these fluvial networks after panning were first studied under an electron microscope in order to evaluate their morphological features and subsequently embedded in epoxy resin, polished, and their compositions determined by both electron microprobe (EMPA) and laser ablation (LA-ICP-MS) techniques. The Lom grains are irregular to sub rounded with extensively pitted surfaces while the Nyong grains are predominantly rounded, oblong and with smooth surfaces. Nyong grains are devoid of inclusions while galena and pyrite are entombed in the Lom grains. Both set of grains are essentially Au–Ag alloys although the Ag content of the cores of the Nyong grains from both EMPA and LA-ICP-MS analytical techniques are significantly lower (0.05–6.07 wt% Ag; 93.54–99.29 wt% Au) than for Lom gold (0.06–22.75 wt% Ag; 78.76–99.86 wt% Au). X-ray element distribution maps do not show any zonal variation in core composition suggesting the gold grains derived from lode sources with single episode of hydrothermal gold deposition. Also the Nyong grains have significant amounts of Pt, Pd and Cr suggesting a link with ultramafic rocks while the Lom grains have substantial Sb and Zn levels pointing to hydrothermal quartz veining as the possible primary mineralization system. The grains from both localities have Ag-depleted rims. The results demonstrate that the microchemical signature of gold is useful to study the hypogene environment of a given area and a field for hydrothermal-orogenic gold is proposed on the ternary Au–Ag–Hg and Au–Ag–Cu plots.

International Journal of Geosciences, 2014

Stream sediments are widely employed in reconnaissance exploration for gold especially in areas w... more Stream sediments are widely employed in reconnaissance exploration for gold especially in areas where outcrops are scarce and the overburden thick such as in the eastern Cameroon goldfields. In this study, 337 stream sediment samples were collected from the Lom river drainage basin. The study aims at identifying the main geological processes affecting the geochemical data from the sediments by considering the multi-elements relationships and spatial features of single elements. The samples were collected in duplicate. One set was panned, gold grains picked and weighed while the second set was wet sieved and the ≤100 microns size fraction retained. This fraction was eventually analyzed for gold by fire assay and a suite of elements by inductively coupled plasma mass spectrometry (ICP-MS). Single element maps were constructed using ArcGIS and the relationship between elements measured using Pearson correlation and principal component analysis (PCA). Gold concentrations in the samples are erratic, most below the detection limit and attain a high of 450 ppm. Five factors are derived from the PCA including single element factors for As and Au reflecting bedrock-hosted mineralization. The Cu-Zn-Y-Nb-Pb factor suggests sulphide mineralization perhaps related to felsic intrusions while the Sr-Ba-LaCe -Zr factor is linked to lithologic control. These results demonstrate the usefulness of multi-element analysis and data interpretation using GIS tools in the exploration efforts for gold worldwide.

Geochemistry

Abstract The distribution of gold in the weathering blanket at the Belikombone gold prospect in e... more Abstract The distribution of gold in the weathering blanket at the Belikombone gold prospect in east Cameroon provides insights into gold mobility in the secondary environment and in tropical terrains worldwide. Both gridline-controlled sampling of topsoil (surface samples) and sampling of various layers in pits are used and the gold assay for each sample determined by NiS fire assay with ICP-AES finish. One hundred and thirty-two (132) surface samples and a total of 206 samples from 19 exploration pits were analyzed. The results from the topsoil samples show an anomaly with the highest Au concentration at 5.9 mgkg-1. The mineralization corridor follows a NE-SW trend. The horizons within the pits range from sap rock at the base, through saprolite, rubble layer rich in relict quartz material to a ferruginous loose layer at the top although some horizons are missing in some pits. All the layers contain gold and the highest concentration in the sap rock horizon is 3.4 mgkg-1 while the rubble layer has a gold high of 6.1 mgkg-1. The individual soil horizons show no systematic gold trends and given the presence of gold in all layers, the patterns point towards supergene dissolution and redistribution of gold. Gold enrichment within the upper horizons in the weathering blanket is attributed to sequestration by Fe oxides of chemically remobilized gold. However, the high gold content within the sap rock and saprolite layers suggests that migration of gold in the particulate form supersedes chemical gold redistribution. Particulate gold obtained by panning samples from the pits varies in shape from euhedral, elongated to irregular. Electron microprobe analysis on the grains record high contents of gold in the rim zones (90.0 to 99.8 wt%). The cores are relatively rich in Ag (12.6 to 14.2 wt%) while the rims are poor in Ag. The low Ag content in the rims is attributed to the preferential leaching of Ag. The soil pH value in this area varies between 3.6 and 7.3. Under such acidic to near neutral conditions, bisulfide and thiosulfate ions can dissolve and transport Au and Ag to be precipitated under surficial conditions creating authigenic Au haloes especially in the saprolite and sap rock layers. Such pH values together with oxidizing Eh conditions explain the solubility of gold in the area. These results are important for geochemical exploration of gold in tropical terrains, and confirm previous studies.

The distribution of gold in the weathering blanket at the Belikombone gold prospect in east Camer... more The distribution of gold in the weathering blanket at the Belikombone gold prospect in east Cameroon provides insights into gold mobility in the secondary environment and in tropical terrains worldwide. Both gridline-controlled sampling of topsoil (surface samples) and sampling of various layers in pits are used and the gold assay for each sample determined by NiS fire assay with ICP-AES finish. One hundred and thirty-two (132) surface samples and a total of 206 samples from 19 exploration pits were analyzed. The results from the topsoil samples show an anomaly with the highest Au concentration at 5.9 mgkg-1. The mineralization corridor follows a NE-SW trend. The horizons within the pits range from sap rock at the base, through saprolite, rubble layer rich in relict quartz material to a ferruginous loose layer at the top although some horizons are missing in some pits. All the layers contain gold and the highest concentration in the sap rock horizon is 3.4 mgkg-1 while the rubble la...

International Journal of Geosciences, 2012

Exploration for primary gold in tropical settings is often problematic because of deep weathering... more Exploration for primary gold in tropical settings is often problematic because of deep weathering and the development of a thick soil cover. In this paper we present the results of both chargeability and resistivity surveys carried out over the Belikombone hill gold prospect (14˚00'-14˚25'E, 5˚25'-6˚00'N) in the Betare Oya area (eastern Cameroon), where previous soil sampling had identified gold anomalies. The geophysical data were obtained using Syscal Junior 48 resistivity meter and the Schlumberger configuration array for both the vertical electrical soundings (VES) and horizontal profiling. These data were further built into a GIS framework and the continuity of favourable gold-bearing structures at depth modeled using WINSEV, RED2INV and SURFER extensions softwares. IP (Induced Polarization)-chargeability and resistivity data combined, have identified irregular anomalous zones trending NE-SW. This trend is consistent with the attitude of most auriferous quartz veins exposed in artisanal pits and parallel to the regional shear zone system and foliations. The high resistivity anomalies correspond to quartz veins while the relatively high IP anomalies correspond to low sulphide ± gold concentrations in the quartz veins. Modeling IP-chargeability and resistivity data prepared as contours and 3D maps, culminated to the development of an inferred, irregular and discontinuous mineralized body at depths of up to 95 m. The size and shape of this mineralized body can only later be tested by drilling to ascertain the resource.