Fracture Analysis of Uranium-Bearing Rock in Eko-Remaja Exploration Tunnel at Depth 50-200 Meters, Kalan, West Kalimantan

Remaja Sector is one of the potential sectors of U mineralization at Kalan Area, West Kalimantan. Host rock of the mineralization is metasiltstone and schistosed metapelite. The 618 meters long Eko-Remaja Exploration Tunnel was built in 1980 to understand the character of uranium ore in this sector. The U mineralization in Kalan, West Kalimantan is influenced by the host rock type and fractures formed by regional tectonic. Regionally, ductile and brittle deformation occurs at Kalan. The ductile deformation observed from N 70o E fold plunging 30o NE that generate schistocity plane dipping 70-80o relatively to the north. First brittle deformation resulting open-mode fractures and schistocity planes that later filled by U-rich solution forming U veins, veinlets and breccia mineralization. Later, brittle deformation forming fractures that filled with calcite-gypsum solution afterwards, forming centimetric-desimetric vein and veinlet cutting the U vein. The purpose of this study is to determine the characteristics and main structure that control the U mineralization in the tunnel. The method is by collecting data of fracture such as joints and fault planes, schistosity planes (S1), and bedding plane (S0) together with its cross-cutting relationship at depth 50 - 200 meter from the tunnel mouth which at this interval representing the presence of mineralization in the Remaja Sector. The data then plotted and analyzed on upper hemisphere stereographic projection. Fracture analysis conducted to understand the families of fractures developed and the force direction resulting fractures the tunnel. From the analysis, the mineralization of U in the tunnel controlled by N 280o E fractures that relatively parallel to the schistocity plane as vein and breccia mineralization and analytical fold axis on Eko-Remaja Tunnel is N 73 E° / 30 tilted to E-NE. Joints in the tunnel mainly affected by faults that formed by couple force.