Subsurface and Office Representation in Mining Geology 1027 



The following criteria determine representational colors and their 

 use. Colors used in superposition are either opaque or transparent, de- 

 pending on purpose and desired effect. Metallization color is somewhat 

 opaque, so that sulphides (indicated as either bands or disseminations) 

 may be superimposed on background of either red (quartz) or green 

 (granite) . Alteration colors are transparent, so that when superimposed 

 on colors indicating igneous rocks, the primary rock compositional color 

 is partially visible. 



Colors are meticuously selected, so that when they are superimposed, 

 the resultant effect clearly indicates superposition, rather than one resultant 

 color indicating a primary unaltered rock. Thus, if yellow (alteration) 

 is superimposed on green (granite), the resulting effect must not be a 

 pegmatite yellow-green. 



The colors are in a chromatic progression from dull colors for early 

 effects toward increasingly brilliant colors for late magmatic effects. 

 Color-brilliance progression is parallel with increasing merit of ore-locali- 

 zation criteria. Siliceous differentiates are represented in more brilliant 

 colors. Quartz veins are shown in bright red, and metallization by brilliant 

 purple. A zonation of increasing brilliance (from the periphery toward 

 an ore-area center) results. Favorable areas are, therefore, readily ap- 

 parent. 



Colors denoting similar compositional effects permit qualitative in- 

 tegration and are consequently quantitatively cumulative. Orange, pink, 

 red, and purple are colors similarly based on the presence of red component 

 and are, therefore, cumulative. When each color represents a hydrother- 

 mal phase or type, the red component of all the colors will tend to integrate 

 total hydrothermal effect. 



Igneous rocks of basic composition are indicated by ultramarine. 

 The increasing addition of yellow component for increased acidity pro- 

 duces greens of various shades, grading from blue-green to yellow-green. 

 The various shades represent either over-all composition or phenocrysts. 

 Ultramarine represents a basic rock; augite or olivene, phenocrysts; blue- 

 green is used to indicate either intermediate composition or plagioclase 

 phenocrysts. If a map area is posted with small, blue-green, dash texture 

 having like-colored, larger, interspersed, dash symbols, a phanerite of 

 intermediate composition and porphyritic texture is indicated. If the 

 large interspersed dash symbols are ultramarine, the phenocrysts are basic ; 

 and if yellow-green, the phenocrysts are quartz. A green pencil-colored 

 background superimposed with ultramarine clastic symbols, and large 

 blue-green and small yellow-green dash symbols indicates aphanite por- 

 phyry of rhyolitic composition containing basic clastic material, large 

 plagioclase and small quartz phenocrysts. Since it is not always possible 

 to indicate such detail graphically or pictorially in the field, textural 

 detail and composite composition (indicated on the field sheet by side- 

 note description) are later translated into graphic, pictorial representa- 

 tion on the ofl&ce maps. 



