Geology of the Clinton Creek asbestos deposit, Yukon Territory

Clinton Creek asbestos deposit is situated at 77 kilometres northwest of Dawson City on Clinton Creek in Yukon Territory. Yukon Metamorphic Complex of Ordovician to Devonian age (470 Ma, Rb-Sr date) covers most of the Clinton Creek area. The most prominent metamorphism of the area occurred in Permian time (245 to 278 Ma, K-Ar dates). Based on intensity and style of deformation of ultramafic bodies and country rocks it is suggested that the ultramafic rocks were emplaced probably during the Permian period. Tintina fault is a weak zone along which the alpine ultramafic bodies of Clinton Creek and probably some of the others along and close to the Tintina Trench were tectonically emplaced. These were later folded and metamorphosed with the country rocks. During latest Cretaceous-earliest Tertiary time (64.9 Ma, K-Ar date) the area was intruded by acid intrusive rocks. The youngest undeformed and fresh basalt is probably of Selkirk volcanics equivalent. Three prominent phases of deformation were delineated. Probably the oldest and most complex phase occurred during the Permian, along with the initial movement of the Tintina fault. Small, tight, isoclinal folds are characteristics of this phase. The structural trend (300* to 315') is roughly parallel to the direction of the Tintina Trench. Due to later deformations changes in direction of fold axes of this phase (190* to 350") is common. The second phase of deformation gave rise to large recumbent folds with trends varying from 270" to 290' with southerly vergence. Third phase of deformation gave rise to antiform structure of regional scale. The Porcupine and Snow Shoe ultramafic bodies are mined for chrysotiile asbestos. A few other ultramafic bodies contain appreciable amount of chrysotile-fibre but not of adequate quantity to be mined. Most of the ultramafic bodies are sheared or massive, and are devoid of known chrysotile-fibre. In general, if serpentinization is less than 75 percent there is no chance of commercial mineralization. Fairly intense fractures are essential to provider adequate openings for chrysotile-fibre formation in ore grade concentrations. Chrysotile-fibre bearing serpentinized ultramafic masses within argillite unit or at the contact of argillite and other units seem to carry ore grade or substantial amount of chrysotile-fibre. Evidence of Clinton Creek asbestos deposit mainly supports formation of chrysotile-fibre as fracture filling. Although evidence of fracture filling rather than replacement seems convincing and exists on a wide scale, a few evidence indicates replacement characteristics on minor scale. The main phase of mineralization is believed to occur at the end of Cretaceous when acid intrusive rocks intruded the vicinity of the Clinton Creek area. These intrusions could have provided warm aqueous solution to react with the existing serpentine along fractures. This resulted deposition of chrysotile-fibre in an essentially closed system. Analysis of isotopic dates of the Yukon Crystalline Plateau shows a distinct grouping of igneous activity at mid Cretaceous and latest Cretaceous time. Some isotopic dates of igneous and metamorphic rocks ranging from 135 to 230 Ma show a distinct younging trend away from the Tintina Trench. The trend suggests that the date at the Tintina Trench is about 200 Ma, and 2'50 kilometres perpendicular distance from the trench is 150 Ma. The apparent horizontal rate of isotherm migration is about 0.5 cm/yr. However, more data is required to confirm the speculation that the Tintina Trench represents an extinct geosuture and vanished ocean.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat