50 • Marine Minerals: Exploring Our New Ocean Frontier 



Table 2-3.— Criteria Used in the Assessment of Placer Minerals 



Information required 



Criterion 



Implication^ 



Types and sources 



1. Presence in marine sediments of 

 interest 



2. Mineral presence in onland 

 unconsolidated deposits close to 

 the shoreline 



3. Presence of drowned river 

 channels and strandlines offshore 

 of coastal host rocks 



4. Occurrence in source rock close to 

 shore 



5. Presence of unconsolidated 

 sediments seaward of onland host 

 rocks 



6. Evidence of preglacial regoliths 

 and mature weathering of bedrock 



7. Sea-level fluctuations: 



(i) Transgression 



(11) Stable sea level 

 (iii) Regression 



8. High-energy marine 



9. Previously glaciated 



-I--1-+ Direct evidence 



10. Ice cover 



11. Circulation patterns 



12. Climate 



-(- + + 



+ + 



+ + 

 + 



+ 

 + 

 + 

 + 



+ 



+ 

 + 



Alluvial sediments in seaward 

 flowing watershed in glacial 

 deposit 



With seaward flowing watershed 

 No watershed but previously 



glaciated with offshore ice 



movement 



Liberation of resistant heavy 

 minerals from bedrock for 

 subsequent transportation and 

 concentration 



For preservation of relict fluvial 



placers now submerged 

 For formation of a contemporary 



beach placer 

 For formation of a contemporary 



river mouth placer 

 For formation of a contemporary 



placer 

 For preservation of a relict placer 



Glacial ice tends to scour out, 

 disseminate or bury the heavy 

 minerals 



In some circumstances glaciation 

 liberates heavy minerals and 

 transports them to considerable 

 distance to the offshore 



Generally the longer the ice-free 

 period the greater potential to 

 generate a marine placer 



Important to the maturity of the 

 mineral assemblage 



Onsite bottom samples 



Historical placer mining records, 

 geological reports 



High-resolution seismic surveys, 

 detailed hydrographic surveys 



CANMINDEX geological reports, 

 mining records, topographic 

 maps, surficial geology maps 



Offshore surficial geology maps, 

 seismic records 



Reports of residual deposits and 

 earlier formed regoliths 



Geological reports, air photos, tide 



records 

 Geological reports, air photos, tide 



records 

 Geological reports, air photos, tide 



records 

 Regional wave climates 



Geological reports, surficial 

 geology maps 



Ice cover maps 



Current maps 

 Paleoclimatic maps 



®A relative ranking scheme was adopted to assess the impiications of each factor with regards to the iil^elihood of a placer occurring in the offshore. Favorable indications 

 are as follows: -I- -t- + extremely favorable, + ■¥ + very favorable and, + favorable. Factors likely to detract from the possibility of an offshore placer utilize a similar 

 approach with a negative sign. 



SOURCE: IVIodified from Peter B. Hale and Patrick IVIcLaren, "A Preliminary Assessment of Unconsolidated tvlineral Resources in the Canadian Offshore," CIM Bulletin, 

 September 1984, p. 7. 



Recent studies of heavy minerals in Atlantic con- 

 tinental shelf sediments have found mineral assem- 

 blages in the north Atlantic region dominated by 

 less chemically stable minerals. The relatively im- 

 mature mineral assemblages result from the direct 

 glaciation that the northern shelf recently received. 

 In general, glacial debris is less well sorted and often 

 contains fresher mineral assemblages than sedi- 

 ment, which has been exposed to fluvial transport 



and weathering processes over a long period of 

 time. While data for the north Atlantic region are 

 too limited to be conclusive in terms of potential 

 resources, greater concentrations of heavy minerals 

 are found south of Long Island (figure 2-5). Total 

 heavy mineral concentrations in the middle Adantic 

 region reach 5 percent or more in some areas, and 

 the mineral assemblages show a greater degree of 

 weathering. In comparison to the northern regions, 



