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Author : Bichler, A.J.; Brooks, E.D.; and Bobrowsky, P.T.
Date : 2002.
Title : Sunshine Coast aggregate potential mapping project.
Publication : British Columbia Geological Survey, Geological Fieldwork 2001
Issue :
Page(s) : 403-408.
Abstract
The Sunshine Coast has long been a major producer of aggregate products that are readily consumed by the expanding markets of southwestern British Columbia and those south of the border. As part of an ongoing initiative of resource inventory, the Geological Survey Branch of the Ministry of Energy and Mines has undertaken an aggregate potential mapping project along the Sunshine Coast during the 2001 field season. The project’s goals follow those of earlier studies conducted by the Branch such as the Prince George (Bobrowsky et al., 1996a), Okanagan (Bobrowsky et al., 1998), Nanaimo (Massey et al., 1998), and Sea-to-Sky (Dixon-Warren et al., 2000; Hickin et al., 2001) projects. The desirable outcome of the project is a regional, reconnaissance style survey that will act as a first approximation of aggregate resources within the region. The project will outline exploited and known aggregate resources as well as potential new deposits, in a qualitative manner using distinct landforms. The study area is located in southwestern British Co-lumbia, northwest of Vancouver, and lies entirely within the Sunshine Coast Forest District. The major communities within the study area are Gibsons, Sechelt and Powell River. It is concentrated along the coastline, stretching from Gibsons as far north as the head of Bute Inlet, with the coastline and a variable buffer extending landward, defining the boundaries of the study area. For the most part this buffer is 3 kilometres wide with exceptions being: between Malaspina Peninsula and Saltery Bay where a 5-kilometre buffer is used; all of Sechelt Peninsula; and Gambier, Texada, Nelson, Read, Cortes and West Redonda islands, which are included in their entirety. Subtracted from the total area are ecological reserves, parks and other protected areas that are greater than 500 hectares. This yields a total study area of approximately 310,000 hectares in portions of NTS map sheets 92F/8-10, 92F/15-16, 92G/5-6, 92G/11-13, 92J/4, 92K1-3 and 92K/6-9. Like most of British Columbia, the majority of the un-consolidated surficial deposits along the Sunshine Coast owe their existence to multiple episodes of glaciation and deglaciation that occurred during the Pleistocene. In partic-ular, it is the most recent cycle of glaciation and deglaciation that has produced the current landscape, and left behind the aggregate deposits that are the subject of this paper. Achange in vegetation approximately 29 ka BP, a result of a deteriorating climate, provides evidence for the onset of the last glacial cycle, the Fraser Glaciation (Clague, 1994). Ice normally restricted to high alpine areas began to expand into and advance down low elevation valleys and fjords. These valley glaciers eventually grew sufficient enough to overtop the confining topography and coalesce into a massive ice sheet known as the Cordilleran Ice Sheet. Outwash sediments associated with these advancing ice fronts are known locally as the Quadra Sands and are found in abun-dance throughout the Strait of Georgia at elevations up to 100 m asl (Ryder and Clague, 1989). These sediments are characterized as being cross stratified, well-sorted, fine to coarse-grained glaciofluvial sands containing minor amounts of gravel and silt (Armstrong and Clague, 1977). Sometime after 25 ka BP, glaciers had reached the Fraser Lowland through valleys entering from the north and east, only to retreat by 19 ka BP (Clague, 1994). Along the Strait of Georgia, an ice lobe spread south well past the Georgia and Fraser Lowlands, achieving its greatest extent by approximately 14.5 ka BP (Mullineaux et al., 1965). As ice overrode the area, sediments collectively known as Vashon Drift were deposited either ice-proximally or in direct contact with ice. These sediments consist of a complex of silty sandy till and sandy and gravelly glaciofluvial and glaciolacustrine sediments (Hicock and Armstrong, 1985). After 14 ka BP, the regional climate began to warm and ice retreat followed, with parts of the Strait of Georgia being ice-free by 13 ka BP(Clague, 1980). The most predominant sediments deposited in the Georgia Lowland during this time are the Capilano Sediments. These are retreat-phase glaciofluvial, glaciomarine and marine sediments deposited on the seafloor, and as raised deltas and intertidal and beach sediments (Armstrong, 1981). Capilano sediments can be found in the region up to an elevation of 180 m asl, indicating a relative sea level much higher than that of present day (McCammon, 1977). Following deglaciation, fluvial and mass wasting processes redistributed glacial sediments during a period of re-adjustment (Ryder and Clague, 1989). Eventually the system evolved into the modern-day scheme, with gravel, sand and silt sediments being deposited in modern fluvial, beach and bog environments; these deposits are known as the Salish Sediments. As this project is still in it’s early stages, results to report at this time are limited to the data capture and compilation stages. During the 2001 field season a total of 98 field stations were visited (see Figure 4). Most sites are located along the coast or near populated areas, rarely more than a couple of kilometres from open water or up a fjord. The primary reason for this is the distribution of surficial sediments within the study area and the added cost of transportation of aggregate products, a limiting factor in the economic viability of an aggregate deposit . The most common sediments extracted in the region are the Capilano Sediments, and is consistent with results from earlier aggregate studies by Leaming (1968) and McCammon (1977). As previously mentioned, these are retreat-phase sediments, consisting of glaciofluvial, glaciomarine and marine sediments deposited away from the glacier fronts. In most cases, pits are located in raised glaciofluvial deltas and consist of interbeded sand, sandy gravel, and gravel at elevations up to 200 m asl. More rarely, Quadra Sand or Vashon till is being extracted. Materials being quarried fall under two categories: granitic rock and limestone, with the greater volume being that of limestone. The granite quarries visited are very small in comparison to the massive limestone operations found on Texada Island (over 6 million tons per year from three quarries). Stockpiles of waste rock at these limestone quarries are a very large potential source of crushed aggregate (in the order of tens of millions of tons). In addition to field data, other major sources of information related to aggregate potential used in this project have included drill logs taken from the Geological Survey Branch’s Assessment Report Index System (ARIS) and water well records from the British Columbia Ministry of Water, Land and Air Protection. Currently there are 455 drill logs and approximately 1300 water well records in the Sunshine Coast Potential Aggregate Mapping Project database. They consist of interbeded sand, sandy gravel and gravel associated with a relict delta. As this project is in it’s early stages, it is not possible at this time to comment on aggregate resource potential along the Sunshine Coast. However, some observations on the ag-gregate industry along the Sunshine Coast can be reported: 1. Glaciofluvial sediments, thought to belong to the Capilano Sediments, are primarily being mined; 2. Mined aggregate deposits lie predominantly below 200 metres asl; and 3. Aggregate pits tend to be near urban centers or near trans-portation routes such as major roads or waterways. Once terrain polygons have been digitized, the compiled data will be spatially referenced to the polygons, and an algorithm will be run on this data to rank the polygons in terms of aggregate potential. The release of results from this project is anticipated in spring of 2002.
Bibliography of Canadian Geomorphology