Subsurface and Office Representation in Mining Geology 1023 



deformational effects (intrusive, metamorphic, or hydrothermal 

 facie), represented by effective colorimetric geologic mapping 

 facilitates source point determination. 



b. Structural Control: Structural location, shape, and attitude 

 exercise a controlling effect on ore localization. 



c. Lithologic Control: Ore deposits are localized where certain 

 wall-rock types occur. Subtle and slight variations in facias 

 may decisively affect ore localization. The lithologic localiza- 

 tion may be determined by 



Compositional Variations, indicated by color (magmatic 

 effects) and pattern (sedimentary rocks) 



Textural Variations, represented independent ^f compo- 

 sition. 



d. Stratigraphic Controls: Ore is often found in equivalent 

 stratigraphic units. Although lithology of the unit may re- 

 gionally vary from quartzite to limestone, there is an unmis- 

 takable tendency for ore localization within the particular 

 stratigraphic unit. No physical or chemical factor has been 

 determined explaining this ore localization. Stratigraphic rep- 

 resentation is independently superimposed on lithologic repre- 

 sentation. 



2. Simplicity of Representation: Similar effects are represented by 

 similar colors or texture symbols. Texture symbols are suggestive 

 of the textures represented. Texture symbols and colors are in 

 gradational systematic sequence corresponding to the textural and 

 compositional classification of magmatic rocks and effects, (fig. 

 541) 



3. Flexibility: Lithology is indicated by combinations of color and 

 texture. Symbols and colors may be proportionately blended to 

 graphically and colorimetrically represent slight facies variations, 

 gradations, and composite textures and compositions. 



4. Permissible Detail: A primary objective of "hard rock" geologic 

 mapping is a maximum representation of detailed data. 



5. Time Sequence: The representation legend shown in figure 541 is 

 based on a systematic colorimetric arrangement parallel to nor- 

 mal time sequence. 



Structure Representation — Compositional structure-dip symbols are 

 posted contiguously to the lithic representation whenever possible. 



Planar structure is indicated by double-barbed dip arrow and posted 

 contiguously to and attached directly to a bed, fault clay, vein, igneous- 

 flow layer or other lithic bands. Planar mineral or clot orientation is in- 

 dicated by flow symbol. 



Linear structure is indicated by half-barbed arrows showing the 

 bearing and inclination of linear structures (striations, flutings, fold-axis 

 lines, minerals, clots, and xenoliths) . In representation, crystalline-rock- 



