Aggregate Resource Potential of the Prince George Area - Digital Data

This file (legend.txt) details the methodology and procedures used in determining the 
aggregate resource potential of the Prince George Area (NTS sheets 93G/10, 14, 15, 16 
and 93J/02).  It is derived from the legends of the five maps (scale 1:50,000) released as:

	P.T. Bobrowsky, PGeo, N.W.D. Massey, PGeo., and A. Matheson, PGeo. (1996); 
		Aggregate Resource Potential of the Prince George Area, B.C. Ministry 
		of Employment and Investment, Open File 1996-24.

These are defined as Level III aggregate resource potential maps (Bobrowsky et al., 1996).


Assessment of Aggregate Resource Potential

Within the Prince George area, 321 individual areas (polygons) have been identified as 
significant for hosting potential natural aggregate resources.  The polygons are based on 
soil and landform units identified and delineated by Farstad (1976a,b,c,d,e) and Dawson 
(1989).  The potential has been assessed by compiling data pertaining to 7 geological 
factors for each of the original 1107 landform polygons within the study area.  Each factor 
was subdivided into several classes and a ranking assigned (see table below and Bobrowsky et 
al., 1996).  Data for factors and rankings have been included as attributes for the landform 
polygons (landform.dbf).

Geological Factors
The factors used to assess the relative potential of an area to host an aggregate deposit are:
1) Landform type: aggregate deposits are formed in certain favourable environments which can 
	be interpreted from the resulting landforms.  The ranking was assigned for both major
	(Landform1) and secondary (Landform2) landform designations within an area 
	(rankings - Lfm1 and Lfm2).
2) Soil type: The soil association developed upon a landform has been rated by Dawson (1989, 
	Table 6) for its suitability as a local source of aggregate.  Gravel and sand were 
	ranked independently for both dominant (Soil1) and secondary (Soil2) soil associations 
	(rankings - Grav1, Sand1, Grav2 and Sand2), although only the gravel rankings were 
	considered in the final analysis.
3) Area: the areas of non-water landform polygons range from 0.36 to >8,000 ha (Area).  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.
4) Pits: a polygon was ranked for the presence or absence of aggregate pits or reserves 
	within it (Pit).  No importance was attached to actual numbers of pits within a 
	landform polygon.  Where a pit or reserve overlapped two or more polygons, all of the 
	latter were ranked as that pit being present.
5) Overburden thickness: The thickness of the overburden which must be removed before 
	extraction of the aggregate is an important factor in evaluating the economic 
	importance of a potential deposit.  Two separate databases yielded information on 
	overburden:
		i) Ministry of Transportation and Highways geotechnical data for its pits 
			and reserves (rankings - Ob_p))
		ii) Drill logs for water wells (data - Overburden; rankings - Over_thick)
6) Gravel Thickness and Volume: Where gravel is known to be present, the size of the gravel 
	unit is important for determining its economic value.  However, very few volume 
	estimates are available within the study area, but thickness can be a useful surrogate. 
	Again two databases yielded information:
	i) Ministry of Transportation and Highways geotechnical data (rankings - Gravel_p; 
		Volume_p)
	ii) Drill logs for water wells (data - Gravel _thi; rankings - Thick_rank)

Final Rankings

The final ranking of the landform polygons was achieved in a two-step process.

First, 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 for either lfm1, lfm2, grav1, grav2, gravel_p, or thick_rank greater 
than 2.  From this subgroup, those polygons with over_rank equal to 1 were eliminated.

Second, for the retained favourable polygons a weighted final rank score was calculated:

	Total Rank = 3*lfm1 + 3*lfm2 + 3*thick_rank + 2*over_rank + 3*pit + area + volume_p

Values for the 321 polygons ranged from 19 - 66.  The significance of a polygon for aggregate 
resources was assigned:

	Primary potential (class=1): Total Rank > 35
	Secondary potential (class=2): Total Rank 31 - 35
	Tertiary potential (class=3): Total Rank < 31

For the whole project area, 61 polygons are of primary, 207 of secondary and 53 of tertiary 
potential.  These comprise 11.8%, 9.2% and 6.0%, respectively, of the total map area.

All other polygons are unclassified (class = U).


Table 1: Summary of values used to determine rankings of individual parameters

	Ranking      Landform       Gravel/Sand      Area            Pit   Overburden
	                                                                     (Pit)
	   5        Fluvial            Good         >535 ha           -	    -	
	            Glaciofluvial
	   4        Lacustrine      Fair to good   216 - 535 ha       -     0 - 1 m
	              beaches
	   3        Ablational Till    Fair         94 - 215 ha       -     1 - 2 m
	            Basal Till
	            Colluvium
	   2            -           Poor to Fair   34.5 - 93 ha       -       >2 m
	   1        Lacustrine         Poor          <34.5 ha       present unknown
	            Organic
	   0        Water            Unsuitable     (all water      absent     -
	                                             polygons)


	Ranking     Overburden   Thickness     Thickness           Volume 
	              (Well)       (Pit)         (Well)             (Pit)
	   5         0 - 3 m       >10 m          >85m          >1,000,000 m3
	   4         4 - 6 m      8 - 9 m      56 - 85 m     500,000 - 
	                                                         1,000,000 m3
	   3         7 - 15 m     6 - 7 m      36 - 55 m      50,000 -
	                                                           500,000 m3
	   2        16 - 44 m     4 - 5 m      16 - 35 m       5,000 -
	                                                            50,000 m3
	   1          >44 m       2 - 3 m       0 - 15 m         0 - 5,000 m3
	   0         unknown      0 - 1 m        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:
	Dawson, A.B. 1989; Soils of the Prince George - McLeod Lake Area, Ministry of 
		Environment, Lands and Pakrs, MOE Technical Report 29.
	Farstad, L. 1976a; Soils and Landforms, Red Rock (93G/10), Ministry of Environment, 
		Lands and Parks, Map, scale 1:50,000.
	Farstad, L. 1976b; Soils and Landforms, Isle Pierre (93G/14), Ministry of Environment, 
		Lands and Parks, Map, scale 1:50,000.
	Farstad, L. 1976c; Soils and Landforms, Prince George (93G/15), Ministry of 
		Environment, Lands and Parks, Map, scale 1:50,000.
	Farstad, L. 1976d; Soils and Landforms, Wansa Creek (93G/16), Ministry of Environment, 
		Lands and Parks, Map, scale 1:50,000.
	Farstad, L. 1976e; Soils and Landforms, Salmon Valley (93J/02), Ministry of Environment, 
		Lands and Parks, Map, scale 1:50,000.

Aggregate Pit locations and geotechnical data:
	Geotechnical and Materials Branch, Central/North East Regional Office, Ministry of 
		Transportation and Highways, Prince George (enquiries phone: 250-565-6185).
	Matheson, A., Massey, N.W.D., Bobrowsky, P.T., Kilby, C.E. and Manson, G.K. 1996; 
		Aggregate Inventory of British Columbia - Private Pits, Ministry of Energy,
		Mines and Petroleum Resources, Open File 1996-5.

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. 








