Aggregate Resource Potential of the Nanaimo Area - Digital Data This file (legend.txt) details the methodology and procedures used in determining the aggregate resource potential of the Nanaimo Area (parts of NTS 92B12, 92B13, 92C09, 92C16, 92F01, 92F02, 92F07, 92F08, 92G04). The 1:50,000-scale data are defined as Level III aggregate resource potential maps (Bobrowsky et al., 1996). The results are published in digital form only and should be cited as: Massey, N.W.D., PGeo., A. Matheson, PGeo., and P.T. Bobrowsky, PGeo, (1998); Aggregate Resource Potential of the Nanaimo Area (parts of NTS 92B12, 92B13, 92C09, 92C16, 92F01, 92F02, 92F07, 92F08, 92G04); B.C. Ministry of Energy and Mines, Open File 1998-12 (digital data). Assessment of Aggregate Resource Potential Within the Nanaimo area, 1394 individual areas (polygons) have been assessed for hosting potential natural aggregate resources. The polygons are based on landform units identified and delineated by Alley (1975, 1977), Cotic (1975), Jungen (1975a,b), Lacelle (1975a,b) and Senyk (1975a,b), with additions and modifications by the authors. The potential has been assessed by compiling data for each of the original 1394 landform polygons. Each parameter contained several classes used to rank polygons (see table below and Bobrowsky et al., 1996). Data for factors and rankings have been included as attributes for the landform polygons in the digital files. Geological Factors The factors used to assess the potential of a polygon to host aggregate are: 1) Landform type: aggregate deposits occur in certain favourable environments which can be interpreted from the observable landforms. The ranking was assigned for both major (Lfm1) and secondary (Lfm2) landform designations within an area (rankings - Lfm1_rank and Lfm2_rank). 2) Area: the areas of non-water landform polygons range from 0.02 to 3858.6 ha (Polyarea). They have been ranked (Area_rank) such that roughly equal numbers of landform polygons fall within each group. No allowance has been taken for partial polygons that occur at the edges of the project area. 3) Pits: each polygon was ranked for the presence or absence of aggregate pits within it (Pit_rank). No importance was attached to the actual numbers of pits within a polygon (Pits). 4) Overburden thickness: The thickness of overburden which must be removed before extraction of aggregate can occur, is an important factor in evaluating the economic importance of a potential deposit. Data are derived from drill logs for water wells (data - Overburden; rankings - Over_rank) 5) Gravel Thickness: Where gravel is known to occur, the amount of gravel is important for determining economic value. However, very few volume estimates are available within the area, but thickness of gravel can be a useful surrogate. Estimates are derived from drill logs for water wells (data - Gravel; rankings - Grav_rank) **********Final Rankings The final ranking of the landform polygons was achieved in a three-step process. First, all polygons (48) which host present or historical aggregate pits were separated out and assigned a classification "H". These represent 6.75% of the total classified area (3.44% of the number of polygons). Second, unfavourable polygons were eliminated based on the rankings for those parameters considered most important for indicating aggregate resource potential. Retained were those polygons with values of greater than 2 for lfm1_rank or lfm2_rank or grav_rank. From this subgroup, those polygons with over_rank equal to 1 were eliminated. Eliminated polygons (395) are classified "U" (Unclassified). They comprise 23.26% of the total area (28.26% of the number of polygons). Third, the retained polygons (951), deemed most favourable to host undiscovered aggregate deposits, were subdivided into three categories based on the weighted final rank score: Total Rank = 3*lfm1_rank + 3*lfm2_rank + 3*grav_rank + 2*over_rank + 3*pit_rank + area_rank Values for the polygons ranged from 13 - 52. The significance of a polygon for aggregate resources was assigned: Primary potential (class=1): Total Rank > 33 Secondary potential (class=2): Total Rank 24 - 33 Tertiary potential (class=3): Total Rank < 24 For the whole project area, 75 polygons are of primary, 229 of secondary and 647 of tertiary potential. These comprise 7.31%, 12.84% and 49.85%, respectively, of the total map area (5.38%, 16.43 and 46.41% of the number of polygons). Table 1: Summary of values used to determine rankings of individual parameters Ranking Lfm Area Pit (ha) 5 Glaciofluvial >679 - 4 Fluvial 398 - 679 - 3 Moraine 238.6 - 398 - Glaciomarine 2 Marine 132.3 - 238.6 - Colluvium 1 Anthropomorphic <132.2 present Bedrock Organic 0 Water (all water absent Unknown polygons) Ranking Overburden Thickness (Well) (Well) 5 0 - 1 m >27m (0 - 3') (>87') 4 1 - 2 m 17 - 27 m (3 - 6') (55 - 87') 3 2 - 5 m 10 - 17 m (6 - 16') (33 - 55') 2 5 - 10 m 5 - 10 m (16 - 33') (15 - 33') 1 >10 m 0 - 5 m (>33') (0 - 15') 0 unknown unknown Notes: Aggregate resource potential maps provide guidelines for testing, evaluating and managing aggregate resources within a defined area. The maps are intended to provide first approximation estimates of broad, regional aggregate distribution. Areas are ranked for their potential to host natural aggregate deposits (mainly gravel). Neither sand deposits nor crushed rock were considered. Detailed groundwork, including mapping, drilling and geotechnical evaluation, is required to further locate, outline and estimate the quantity and quality of the deposit before its economic significance can be evaluated. Rankings, both for individual parameters and final total ranking, are relative between areas within the project and cannot be compared directly to results from other study areas. All data were used as presented by the agency responsible for a particular database. The accuracy and integrity of those data are assumed. The authors and the Geological Survey Branch are not responsible for inaccuracies, omissions and errors resulting from this work. Sources of Information: Soils and landforms: Alley, N. 1975; 92C/09, San Juan, Terrain (Landforms); Ministry of Environment, Resource Analysis Branch. Alley, N. 1977; 92C/16, Cowichan Lake, Terrain (Landforms); Ministry of Environment, Resource Analysis Branch. Cotic, I. 1975; 92G/04, Nanaimo, Terrain (Landforms); Ministry of Environment, Resource Analysis Branch. Jungen, J. 1975a; 92F/01, Nanaimo Lakes, Terrain (Landforms); Ministry of Environment, Resource Analysis Branch. Jungen, J. 1975b; 92F/08, Parksville, Terrain (Landforms); Ministry of Environment, Resource Analysis Branch. Lacelle, L. 1975a; 92B/13, Duncan, Terrain (Landforms); Ministry of Environment, Resource Analysis Branch. Lacelle, L. 1975b; 92F/07, Horne Lake, Terrain (Landforms); Ministry of Environment, Resource Analysis Branch. Senyk , J. 1975a; 92B/12, Shawnigan, Terrain (Landforms); Ministry of Environment, Resource Analysis Branch. Senyk , J. 1975b; 92F/02, Alberni Inlet, Terrain (Landforms); Ministry of Environment, Resource Analysis Branch. Polygons from these 1:50,000-scale maps have been digitized and made available from the Digital Terrain Map Website: http://www.ei.gov.bc.ca/geosmin/terrain/frbc.htm Water well data: Water Management Division, Ministry of Environment, Lands and Parks, Victoria. (enquiries phone: 250-387-9483 or via Internet at http://wtrwww.env.gov.bc.ca/wat/gws/gwis.html) Other references: Bobrowsky, P.T., Massey, N.W.D. and Matysek, P.F. 1996; Aggregate Forum, Developing an Inventory that Works for You!, Report of Proceedings, Ministry of Energy, Mines and Petroleum Resources, Information Circular 1996-6.