The Central Africa Fold Belt(CAFB)is a collision belt endowed with gold deposits in Eastern Cameroon area mined for about 50 years.However,favorable areas for gold exploration are poorly known.This paper presents(1)th...The Central Africa Fold Belt(CAFB)is a collision belt endowed with gold deposits in Eastern Cameroon area mined for about 50 years.However,favorable areas for gold exploration are poorly known.This paper presents(1)the kinematics of the brittle deformation in the Kékem area in the SW portion of the Central Cameroon Shear Zone and(2)constraints gold mineralization events with respect to the collisional evolution of the CAFB.The authors interpret that the conjugate ENE to E and NNW to NW trending lineament corresponds to the synthetic(R)and the antithetic(R’)shears,which accompanied the dextral slip along the NE to ENE striking shear.The latter coincides with the last 570-552 Ma D3 dextral simple shear-dominated transpression,which is parallel to the BétaréOya shear zone hosting gold deposits.Gold mineralizations,which mainly occurred during the last dextral shearing,are disseminated within quartz veins associated to Riedel’s previous structures reactivated due to late collisional activities of the CAFB as brittle deformation.Gold mineralizations occurred mainly during the 570-552 Ma D3 event.The reactivation,which might be due to dextral simple shear during mylonitzation,plausibly remobilized the early gold deposits hosted in syn-compressional rocks and/or possibly focused deep-sourced fluid mixed with those released by dehydration.Therefore,the Central Cameroon Shear Zone where Kékem is located,and which shows similar petrographical and structural features to those controling Batouri gold district,is a target area for gold exploration in Cameroon.展开更多
The regions with shear stress and mean velocity gradient of opposite sign often exist in complex turbulent shear flows.In these cases,the eddy viscosity hypothesis breaks down.Hinze regards the,departure from eddy vis...The regions with shear stress and mean velocity gradient of opposite sign often exist in complex turbulent shear flows.In these cases,the eddy viscosity hypothesis breaks down.Hinze regards the,departure from eddy viscosity hypothesis as a result from transportation of mean momentum over distance by the large structures and arrives at a shear stress expression including the second order derivatives of the mean velocity.However,his expression greatly overestimates the shear stress.This implies that the flow particles are unlikely to have enough memory of the mean momentum over distance.By assuming the departure from eddy viscosity hypothesis as a result from transportation of the shear stress contained in smaller eddies over distance by the large structures,the present author has arrived at a new shear stress expression.The shear stress estimated so far is in good agreement with the experiments.展开更多
文摘The Central Africa Fold Belt(CAFB)is a collision belt endowed with gold deposits in Eastern Cameroon area mined for about 50 years.However,favorable areas for gold exploration are poorly known.This paper presents(1)the kinematics of the brittle deformation in the Kékem area in the SW portion of the Central Cameroon Shear Zone and(2)constraints gold mineralization events with respect to the collisional evolution of the CAFB.The authors interpret that the conjugate ENE to E and NNW to NW trending lineament corresponds to the synthetic(R)and the antithetic(R’)shears,which accompanied the dextral slip along the NE to ENE striking shear.The latter coincides with the last 570-552 Ma D3 dextral simple shear-dominated transpression,which is parallel to the BétaréOya shear zone hosting gold deposits.Gold mineralizations,which mainly occurred during the last dextral shearing,are disseminated within quartz veins associated to Riedel’s previous structures reactivated due to late collisional activities of the CAFB as brittle deformation.Gold mineralizations occurred mainly during the 570-552 Ma D3 event.The reactivation,which might be due to dextral simple shear during mylonitzation,plausibly remobilized the early gold deposits hosted in syn-compressional rocks and/or possibly focused deep-sourced fluid mixed with those released by dehydration.Therefore,the Central Cameroon Shear Zone where Kékem is located,and which shows similar petrographical and structural features to those controling Batouri gold district,is a target area for gold exploration in Cameroon.
文摘The regions with shear stress and mean velocity gradient of opposite sign often exist in complex turbulent shear flows.In these cases,the eddy viscosity hypothesis breaks down.Hinze regards the,departure from eddy viscosity hypothesis as a result from transportation of mean momentum over distance by the large structures and arrives at a shear stress expression including the second order derivatives of the mean velocity.However,his expression greatly overestimates the shear stress.This implies that the flow particles are unlikely to have enough memory of the mean momentum over distance.By assuming the departure from eddy viscosity hypothesis as a result from transportation of the shear stress contained in smaller eddies over distance by the large structures,the present author has arrived at a new shear stress expression.The shear stress estimated so far is in good agreement with the experiments.