ORE DEP (VOLCANISM) Flashcards
Hydrothermal deposits formed at low temp (100-320 deg cel) usually at shallow depths (<2km)
Epithermal Gold
Usual Ore minerals in Epithermal Systems
Native Gold
Silver
Tellurides and Sulfosalts
Usual Gangue in Epithermal Systems
Qtz ad Chalcedony
Carbonates
Fluorite
Barite
Sericite
Adularia
Clay
Common Textures of Ore minerals
Banded
Drusy
Comby
Crusty
Vuggy
Colloform
Alteration
Widespread Chloritic, Sericite, Qtx and Pyrite
Local Carbonates and Felds
Lindgrens Classification
Classification
1) Epithermal
2) Mesothermal
3) Hypothermal
Arc type ephitermal deposits
1) High Sulfidation
2) Int Sulfidation
Rift Type Epitherma system
Low Sulfidation
Bimodal Volcanism Related LSE
Alkalic LSE
Types of Epithermal Gold
pH
High Suplhidation
1-3 (Acidic)
Intermediate Sulphidation
5 (Mod Acidic)
Low Sulphidation
4-6 (Mildly Acidic)
Low Sulphidation Alkalic
> 6Basic
?sulfur is in very high oxidation state of +4 because of the dominance of magmatic SO2
?formed when very acidic fluids dominated by reactive magma derived gases migrate vertically along the sturtcure and permeable country rock and under fliuid reaction and fluid mixing
?generated in Calc-Alkaline Andesitic to Dacitic Arcs
?Near Neutral stress or Mild Extension
?Genetically linked to underlying PCD
?Cannot be related to Rhyolite
High Sulfidation
Indicative Minerals of High Sulifidation
Energite
Luzonite
Tennantite
other names for High Sulfidation
Acidic Sulfate
Qtz-Alunite-Enargite Gold
Silica-Kaolinite +/- Pyrphyllite Gold
Characteristics of High Sulfidation Epithermal
?Zoned Central Advance Argillic - Argillic to peripheral Prophylitic Alteration Zones
?Cu-Au-As Mineralozation common with Enargite /luzonite as dominant Cu Mineral phase and associated with Vuggy Silica
?Assoc with Calc Alkaline Volcanism
Example of High Sulfidation
Lepanto
Nalesbitan Cam Norte
IN what type of volcanism does Intermediate Sulfidation usually occurs?
Calc Alkaline Andesitic to Dacitic Arc
locally may be hosted in more felsoc rocks
Difference of Intermediate from High Sulfidation
Unrelated to PCDs and can be hosted by Felsic or Rhyolitic Rocks
Largest intermediate Sulphidation deposits
FSE-Lepanto-Victoria, Mankayan
Other Intermediate Sulphidation in the Philippines
Acupan and Antamok Deposits, Baguio
Diwalwal, Comval
Maco
Aroroy
Co-O
Formed when Magmatic fluids w/c contain dissolved reactive gas are REDUCED by rock reaction and dilution by the mixing with circualating meteoric Waters resulting in a FLUID DOMINATED by DISSOLVED SALTS and H2S as the MAIN SULFUR SPECIES
Low Sulfidation Epithermal
In what type of tectonic environemnts are low sulfidation generated?
Rift typpe (Continental or Island Arcs)
Low Sulfidation Minerals
Galena
Sphalerite
Chalcocite
Two types of Low Sulfidation
1) Bimodal Volc
2) Alkaline
LSE which is related to alkaline magmatism and is capable of generating Porphyry Cu-Au Deposits
Formed at Moderated saline fluids
High Temp >300 deg cel
Alkaline Low Suphidation
Example of Alkline Low Sulphidation in the Philippines
Marian Isabela
Didipio, Neva Vizcaya
LSE deposits found in various rift setting such as Intra-Arc, Near Arc or Back Arc during cessation of subduction and post collitional Settings
Bimodal Related LSE
waning, retreat and steepening of the downgoing tectonic plate during subduction which can transform Earth’s surface by altering the stresses on the overriding plate.
Slab Rollback
Rifting which may create Slab Windows
Oblique Subduction
Gravitaional controlled lateral expansion of thiceknd crust followinge episodes of contractional deformation./Compression
Tectonic Collapse
Riftingc caused by mantle Plume activity
Hot Spot
Processes which may cause rifting
1) Slab RollBack
2) Slab Break off
3) Obliqe Subduction
4) tectonic Collapse
5) Hotspots
? the invisible gold deposit or sediment hosted replacement Gold considered as low sulphidation epithermal Fluids in reactive carbonate rocks
Carlin Type Gold
Morphology or teture of Carlin Type Gold
Very Fine Grained
Disseminations
Host rocks
Carbonaceous Calcaerous Rocks
Jasperoids
Examples
?Carlin, Nevada USA
?Bau, Malaysia
?Mesel, Indonesia
?Sepon Laos
