SURFICIAL DEPOSITS IN THE LOUIS CREEK AND CHU CHUA CREEK AREA
Surficial geological mapping and drift exploration studies were undertaken in the summer of 1997 north of Kamloops in NTS map sheets 92Pil (Louis Creek) and 92P18 (Chu Chua Creek), as a continuation of the Eagle Bay Project initiated in the previous year (Bohrowsky et al., 1997; Dixon-Warren er al., 1997). The surticial component is pat of an integrated regional study centred on Devono-Mississippian rocks of the Eagle Bay Assemblage and Permian to Devonian rocks of the Fennell Formation. Massive sulphide deposits hosted in stratiform volcanogenic assemblages of the Fennell Formation at Chu Chua (MINFILE 092P 140) and syngenetic sedimentary rocks of the Eagle Bay Assemblage at Mount Armour (MINFILE 092P 051) suggest the region has considerable mineral potential. Polymetallic gold-bearing veins hosted in volcanic and volcanogenic rocks of the Fennel Formation at Windpass (MINFILE 092P 039) also suggest a high potential for gold in the area. Several placer occurrences of Au have also been recorded in the region.
Barkerville Project: Regional Till Geochemistry (93H/4, 5) and Orientation (93A/14) Studies
During the 2000 field season, both regional and detailed till sampling surveys were conducted in the Cariboo region of central British Columbia (Figure 1). These surveys complement the longer term objectives of the NATMAP Ancient Pacific Margin (APM) project (see Nelson, 2000) and provide continuity to the surficial till geochemistry work initiated by Dixon-Warren and Hickin (2000) in 1999 as part of the APM project team. The regional till survey discussed here, represents work in the first of a multi-year, integrated exploration program, hereafter called the Barkerville Project. The Barkerville Project follows a series of previous integrated or focused multi-year Geological Survey Branch initiatives completed throughout the province in areas of high mineral potential (e.g. Northern Vancouver Island 1991-1994; Kerr et al., 1992; Bobrowsky and Sibbick, 1996; Nechako/Fraser Plateaus 1991-1995; Levson and Giles, 1997; Eagle Bay 1996-1998; Bobrowsky et al., 1997; Dixon-Warren et al., 1997; Paulen et al., 1998, 1999). In contrast, the Ace Project is a detailed till orientation study, also located in the Cariboo region, that complements previous orientation and property-scale surveys completed in the province which aim to model site specific behaviour of elements in different types of media (e.g. Cook and Pass, 2000). The Barkerville Project is centred primarily over rocks of the Barkerville and Slide Mountain terranes (Figure 2). This first year of work evaluated till geochemistry in the southern half of NTS map sheet 93H/05 (Stony Lake) and the northern half of 93H/04 (Wells), located directly north of the town of Wells (Figure 1). The study covers an area of approximately 1000 square kilometers. A number of factors provide the impetus for this project area: 1) the high mineral potential of the terranes for lode gold mineralization and placers; 2) the previous successful industry record for locating new showings using till geochemistry farther south in Eagle Bay rocks (also Barkerville Terrane); and, 3) the increasing industry exploration activity and the need for this type of data in the Cariboo region. In the past, placer and lode gold deposits supported the local mining industry in the region, but with the more recent realization of VMS potential, exciting new mineral prospects including the Lottie, Frank Creek and the Bonanza Ledge Zone have come to light. The primary purpose of the multi-year survey is to provide reconnaissance level till geochemistry data and re-
Cleat mineralization of Upper Permian Baralaba/Rangal Coal Measures, Bowen Basin, Australia
Abstract Coals from the Permo-Triassic Bowen Basin have been investigated using a variety of complementary analytical techniques. Face cleat minerals in the studied samples are dominated by authigenic clays, notably pure illite or illite-chlorite mixtures. Butt cleats and joints are dominated by carbonates, mostly calcite with less abundant ferroan calcite, ankerite and siderite. K/Ar ages of cleat-fill illites and one fracture illite-smectite fill indicate three phases of illite formation during the Triassic: (1) an early phase with ages clustered around 244 Ma ago; (2) a second phase about 232 Ma ago; and (3) the latest phase about 219 Ma ago. Thermal modelling of selected boreholes from the study area and other geological data indicate that the first phase of illitization occurred when the coal seams were about 1000 m below the surface and at a temperature of between 70 and 80°C, at a time when the basin was rapidly subsiding. These early illites were stable and retained their 1M polytype even after being exposed to temperatures of 150–190°C during maximum burial in the southeastern Bowen Basin. The second phase of illitization (at 232±3) occurred at about the time of maximum burial. The latest phase took place between 223±3 and 212±3 Ma ago and occurred in a wider temperature range (between 170 and 100°C) during a rapid uplift in the Late Triassic. The Bowen Basin area experienced a second cycle of subsidence that commenced in the Early Jurassic with the formation of the Surat Basin, which overlies the Bowen Basin and forms part of the Great Artesian Basin system. Regional uplift and erosion in middle Cretaceous times terminated sediment accumulation in the Surat Basin. During the second cycle of burial widespread carbonate mineralization in butt-cleats and joints took place. Calcite fluid inclusions indicate that calcite was precipitated from meteoric water at about 80°C. The widespread carbonate mineralization in butt cleats and the near-absence of carbonates in the face cleats is here attributed to permeability anisotropy, caused by a change in the direction of lateral compressive stress during Jurassic-Cretaceous times relative to that during the Triassic Hunter-Bowen Orogeny.