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. 







