The Dimako–Mboscorro lode gold deposit has two styles of mineralization: quartz veins (4.5–54 ppm Au) and altered wallrock (up to 2.6 ppm Au). The veins occur in steeply dipping brittle–ductile shear zones in a foliated biotite metagranite. The alteration envelop around the gold-bearing quartz veins shows lateral zoning comprising a silicified/ ferruginized and mylonitic zone (SFZ) at the centre, through a transitional sericite zone (SZ), to an outer, slightly sheared, but mineralogically less altered, though bleached, metagranite zone (BZ) at the shear zone boundaries. Hydrothermal alteration in these zones is characterized by silicification (SFZ, SZ), hematite formation (SFZ), alkali metasomatism with muscovite/sericite formation (SFZ, SZ, to a much lesser extent BZ), and pyritization (SFZ, SZ). The auriferous quartz veins are concordant to the host structure but discordant to the foliation in the metagranite. The main ore minerals in the veins and in the SFZ and SZ zones are gold, hydrothermal hematite, sphalerite, galena, pyrite, chalcopyrite, arsenopyrite, chalcocite, covellite and colloidal supergene hematite. Gold occurs as inclusions in sphalerite (15.7±0.4 wt% Ag; 83.6±0.2 wt% Au), as coarse grains associated with euhedral hematite pseudomorphs (18.5±1.0 wt% Ag; 82.0±1.1 wt% Au), as stringers within fractures in quartz (13.3±0.1 wt% Ag; 87.1±0.5 wt% Au), as well as fine to coarse grains related to limonite, goethite and colloidal hematite (8.1±1.8 wt% Ag; 92.1±2.2 wt% Au). A hydrothermal metal association of Ag, Au, As, Ba, Pb, V, W, and Zn is identified in the wallrock and quartz veins. These metals, together with K-enrichment, are potential pathfinder elements for wider lithogeochemical exploration in this region, especially when combined with the lateral wallrock zonation pattern. Preliminary fluid inclusion data from the auriferous quartz vein samples indicate that gold was probably deposited from low salinity (<1 to 8 wt% eq. NaCl, with mean at 5.52 wt% eq. NaCl) H 2 O–CO 2 fluids that have total homogenization temperatures of 263–335°C.

A study of environmental chloride and groundwater balance has been carried out in order to estimate their relative value for measuring average groundwater recharge under a humid climatic environment with a relatively shallow water table. The hybrid water fluctuation method allowed the split of the hydrologic year into two seasons of recharge (wet season) and no recharge (dry season) to appraise specific yield during the dry season and, second, to estimate recharge from the water table rise during the wet season. This well elaborated and suitable method has then been used as a standard to assess the effectiveness of the chloride method under forest humid climatic environment. Effective specific yield of 0.08 was obtained for the study area. It reflects an effective basinwide process and is insensitive to local heterogeneities in the aquifer system. The hybrid water fluctuation method gives an average recharge value of 87.14 mm/year at the basin scale, which represents 5.7% of the annual rainfall. Recharge value estimated based on the chloride method varies between 16.24 and 236.95 mm/year with an average value of 108.45 mm/year. It represents 7% of the mean annual precipitation. The discrepancy observed between recharge value estimated by the hybrid water fluctuation and the chloride mass balance methods appears to be very important, which could imply the ineffectiveness of the chloride mass balance method for this present humid environment.

The alluvial aquifer underlying the city of Douala comprises shallow Quaternary deposits where groundwater is the main source for domestic and drinking purposes. Shallow groundwater in the area show signs of acidification with average pH range of 3.8-6.8. Long-term groundwater chemistry data (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013), hydrogeochemical and R mode factor analysis were used to establish the acidification process of shallow groundwater and also determine possible origin and implications for water quality and use in the area. Twenty-six groundwater sample points, three streams and three rain sample points were studied seasonally in the 2006-2008 and the 2010-2013 study periods. The data were compared with result of a study, 7 years earlier (1998)(1999). The results show evidence of acidification manifested by depletion of HCO 3 , a decrease in the pH and increase in SO 4 and NO 3 concentrations of shallow groundwater. Average groundwater pH range is 3.of water samples fall within the range of pH (6.5-8.5) for potable water according to WHO (1993). The alkalinity/acid neutralizing capacity of the shallow groundwater has decreased significantly coupled with increase in the number of zero alkalinities recorded in the 2010-2013. The shallow groundwater is generally undersaturated with common carbonate minerals (calcite, dolomite), therefore providing insufficient acid buffer. Principal component analysis in combination with hydrogeochemical studies revealed that four main factors are responsible for the groundwater chemistry and acidity: (1) acid atmospheric deposition, (2) anthropogenic activities (industrial effluent discharges and acid spill, (3) chemical weathering, and (4) coastal atmospheric deposition/cation exchange. In general, the shallow groundwater is not suitable for drinking and domestic purposes with respect to the low pH and elevated nitrate concentration. In view of the implications such as increase in corrosion and increased mobilization of toxic elements (e.g. Al, Pb, Cu, Zn, Mn) as well as their possible harmful effect on health, it is recommended that the causes, rate of acidification and the mobility of trace elements be investigated with more details.

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The geochemical characterization of Novokrivoyrog metavolcanics (2.2 Ga) and Krivoy Rog iron ores (1.8 Ga) in Ukraine represent an important tool for the understanding of their genesis and tectono-magmatic evolution. The petrological classification of the metavolcanics on SiO 2 /(Zr-TiO 2 ) and (Zr-TiO 2 )/(Nb/Y) Harker-type diagrams shows similarities to subalkaline andesitic basalts. An additional classification of the basalts on TAS (Na 2 O + K 2 O/SiO 2 ) and AFM (FeO-MgO-Na 2 O + K 2 O) diagrams exhibits a variable magmatic character from calc-alkaline to tholeiitic. The distribution of High Field Strength Elements, (HSFE: Ti, Zr, Y, Hf, Nb), V, Cr, and Rare Earth Elements (REE) in most of the rocks is close to calc-alkaline basalts (CAB) and can be compared to Precambrian mid-ocean ridge basalts (MORB) where high thermal (>250˚C) basaltic alteration is intensive under pH conditions between 2 and 4. These contributed to the deposition of the Krivoy Rog BIFs. Indeed REE distribution patterns of the BIFs suggest that they can be subdivided into shales and shaly BIFs (rich in LREEs since their detrital and clastic inputs are much higher) with (La/Yb)N > 1 as indication of clastic inputs; chert and cherty BIFs showing positive Eu anomaly with (La/Yb)N < 1 are similar to REE patterns of mixed hydrothermal fluids and seawater; alkaline altered BIFs whose (La/Yb)N ratio is >1 emphasizes post-depositional effects related to the enrichment of light REEs over heavy REEs with a positive Eu anomaly. The distribution of REE patterns of Krivoy Rog BIFs can finally be compared to Precambrian iron formations of mixed submarine hydrothermal fluids and seawater origin which correspond to the MORB signature of the Novokrivoyrog metavolcanics.