Built by a geologist
Alteration & Mineralization Logging
Alteration and mineralization are the keys to understanding ore deposit geology. Accurate logging of these features guides exploration targeting and resource estimation. Alteration Logging Alteration = mineralogical changes caused by fluids hydrothermal, weathering, metamorphic Common Alteration Types | Type | Key Minerals | Associated Deposits | |------|--------------|---------------------| | Potassic | K-feldspar, biotite | Porphyry Cu-Mo | | Phyllic | Sericite, quartz, pyrite | Porphyry Cu, epithermal | | Argillic | Kaolinite, montmorillonite | Epithermal, porphyry | | Propylitic | Chlorite, epidote, calcite | Porphyry distal | | Silicic | Quartz flooding | Epithermal, VMS | | Carbonate | Calcite, dolomite, ankerite | Orogenic Au, skarn | Alteration Intensity Scale - Weak : <25% original minerals altered - Moderate : 25-50% altered - Strong : 50-75% altered - Intense/Pervasive : 75% altered Logging Format Record: Intensity + Type + Mineralogy Example: "Strong phyllic sericite-quartz-pyrite " Mineralization Logging Sulfide Minerals | Mineral | Formula | Color | Association | |---------|---------|-------|-------------| | Pyrite | FeS₂ | Brass yellow | Ubiquitous | | Chalcopyrite | CuFeS₂ | Golden/brass | Cu ore | | Galena | PbS | Lead gray | Pb ore | | Sphalerite | ZnS | Brown/black/yellow | Zn ore | | Arsenopyrite | FeAsS | Silver-white | Au indicator | | Pyrrhotite | Fe₁₋ₓS | Bronze, magnetic | Ni, Au | Mineralization Description - Mineral species : Identify and list - Abundance : Estimated %, or trace/minor/major - Habit : Disseminated, veinlet, massive, blebby - Association : Co-existing minerals, host rocks - Size : Fine, medium, coarse Mineralization Styles - Disseminated : Scattered throughout rock - Stockwork : Network of thin veinlets - Massive : 50% sulfide - Banded : Layers of sulfide - Replacement : Pseudomorphing original rock Visual Estimation Percent Estimation Chart Practice with standard percentage charts: - 1% = scattered specks - 5% = noticeable but sparse - 10% = common throughout - 20% = abundant - 50% = rock is half sulfide Tip : Cut a 10×10 grid on paper, shade squares to visualize percentages