QUARTZ TEXTURE

QUARTZ TEXTURES - POTENTIAL CLUES TO POSITION AND OR PROCESS IN LS SYSTEMS

Primary Growth Textures : Chalcedonic, Saccharoidal,Comb,Zoned Crystals, Colloform, Crustiform

Recrystallisation Textures : Moss, micro plumose

Replacement Textures : Mold, Bladed


Aqueous silica concentrations are directly influenced by presence of solid silica phases (AMORPHOUS / CHALCEDONY / QUARTZ) and temperature. In long lived systems quartz controls silica solubility >1800C and chalcedony controls silica solubility <900C to 1400C.

Buchanan/Morrison/Corbett & Leach

From mining engineering

Buckskin Mt

From mining engineering

Broadlands Geothermal

From mining engineering

Vera Nancy - Textural Para genesis

From mining engineering

Champagne Pool and sinter

From mining engineering

Champagne Pool, Amorphous silica /mineralized ooze

From mining engineering

80 ppm Au

175 ppm Ag

2%As

2%Sb

320 ppm Tl

170 ppm Hg

Sinter - Waiotapu NZ

From mining engineering

BANDING AND SEDIMENTARY TEXTURES IN VEINS

Simpson et al 1995 describe apparent sedimentary textures such as grading of sulphides/quartz plus ripple marks in banded vertical veins at Golden Cross NZ.

Banding within the quartz veins is primarily a result of variation in quartz grain size. Sulphide minerals and kaolinite are most abundant in fine grained quartz bands that may have been deposited in an amorphous silica state.

These NZ workers interpret observed textures in the following way.

System pressure is breached by fault dilation or hydrothermal eruption resulting in amorphous silica saturation of a rapidly moving fluid. This event is accompanied by upward surge of sulphide rich fluid from deeper in the system. As system pressure resumes via mineral deposition in veins, temperature increases and silica saturation levels return toward quartz. Eventually the higher T/P system deposits sulphide barren quartz from more slowly moving fluid.

Repeated system rupturing leads to formation of banded veins.

USEFUL TEXTURES

Sinter- marks paleo-surface and paleo-water table. Textures distinguish from silicified tuff or lake sediment. NB. no Sinter in HS environment.

Chalcedony - low temperature silica (120o-200oC) usually at shallow depths above an up flow zone and possibly overlying mineralization.

Colloform banding -in chalcedonic quartz-kidney like or rounded external surface from original silica gel. Close association with ore. Downgrade potential if these textures don’t carry grade.

Crystalline quartz -usually occurs in deeper/ hotter part of system at > 180oC though the temperature overlap between quartz and chalcedony means both can occur in same part of a vein. Crystalline Quartz alone likely indicates hot/deep environment > 250oC.

Drusy cavities - void spaces partly filled with terminated crystals (calcite or quartz) are commonly last vestiges of hydrothermal activity.

Lattice textures are indicative of boiling conditions.

Cockade and comb textures - indicate open space filling.

BY CAREFUL OBSERVATION A GREAT DEAL CAN BE LEARNT ABOUT PROCESSES OPERATING AND LIKELY SPATIAL RELATIONSHIPS TO ORE.
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