Subsurface and Office Representation in Mining Geology 1025 



mineral-texture symbols are oriented to show predominate lineation direc- 

 tion; half-barbed arrows are posted contiguously to show horizontal pro- 

 jections and inclinations of maximum elongation lines (fig. 541). 



Non-Compositional structure (schistosity and jointing) is indicated 

 by black lines superimposed on the lithic representation. Schistosity and 

 jointing inclination is represented by unbarbed dip symbols. The repre- 

 sentation is quantitative in that spacing of lines indicates spacing of joints. 

 Two or more systems of joints may be represented in superposition. 



Direction and amount of displacement are indicated whenever ap- 

 parent. On plan maps, positive or up, and negative or down displacement 

 are indicated respectively by plus and minus signs. On sections, move- 

 ment toward and away from the observer are indicated respectively by 

 plus and minus signs. Half-barbed arrows show relative directional dis- 

 placement. Parenthetically enclosed symbols denote apparent displace- 

 ment direction. Amount of displacement is indicated numerically in inches 

 or feet. Parenthetically enclosed numbers denote apparent displacement. 



Texture — Texture is represented by symbol (fig. 541). Textural 

 quantitative, qualitative, and gradational values are shown graphically 

 and relatively by size, shape, spacing, and attitude of symbols. Simple 

 and composite textural combinations are accurately and graphically rep- 

 resented by combinations of symbols. 



The symbol is usually a pictorial representation of indicated texture. 

 Banded, layered, or bedded rocks (sedimentary, metamorphic, igneous) 

 are indicated by parallel lines conformable with attitude and relative 

 width of bands. The clastic symbol (to denote sediments, metamorphics, 

 and pyroclastics) is modified to show relative size, shape (angularity or 

 sphericity), and spacing of clastic material. Solid color represents either 

 soil (if gray) or aphanitic texture. 



Sedimentary rocks are represented on plan and section by black sym- 

 bolic lithic-mapping units. Lithic symbols are proportionately blended 

 and superimposed to show either abrupt or gradational facies variations. 



Metamorphic rocks are represented by black symbols with superim- 

 posed color to indicate magmatic or hydrothermal effects. Closely spaced 

 black lines indicate schistose or micaceous-rock cleavage; the relative line 

 spacing indicates schistose layers. Crystalline or gneissic textures are 

 shown in the same manner as igneous rocks. Facies banding is indicated 

 by compositional color banding. Metacrysts are indicated by phenocryst 

 or phanerite symbols. 



Igneous rock textures are indicated by standardized compositional 

 colored symbols. Two basic media, solid pencil or air brush color indi- 

 cating aphanitic texture and dash symbols indicating phaneritic texture, 

 are sufficient to represent most igneous rocks. The colored-dash symbols 

 superimposed on the solid-color batfcground indicate felsite porphyries. 

 Relative size, attitude, and spacing of phenocrysts or crystals are indi- 



