Fun Facts Flashcards
What percent of the world’s gold production is from Carlin-Type deposits? (2014)
9%
What type of gold does Carlin-type deposits host?
Primary gold that is restricted to ionic substitution and submicron-sized grains in arsenian pyrite.
How are Carlin-Type deposits distinctive from typical epithermal ores? (3 points)
1) Form replacement bodies with structural and stratigraphic controls.
2) Contain primary gold restricted to ionic substitution and submicron grains in asenian pyrite
3) Exhibit alteration that is subtle but dominatted by decarbonatization of silty calcareous host rocks.
How did gold precipitate in Carlin-Type deposits?
Precipitated in response to sulfidation of iron in the host rock or in a second, iron-bearing fluid. NOT from boiling or cooling as it is in most epithermal systems.
What are the three major model classifications for Carlin-Type Deposits?
1) Epizonal Plutons contributing heat and possibly fluids/metals
2) Meteoric fluid circulation resulting from crustal extension scavenged and precipitated metals with or without contributions of heat from widespread magmatism
3) Metamorphic fluids from deep or midcrustal levels, possibly with a magmatic contribution, transported and precipitated metals.
Why is it hard to determine the genesis of Carlin-Type deposits?
1) The complex geologic history of northern Nevada
2) Nevada has also undergone multiple diagentic and hydrothermal events that produce many of the same minerals as Carlin-Type deposits.
3) Supergene alteration oxidized the orebodies and mobilized gold
What minerals make up the main ore stage?
Quartz, Pyrite, Illite, and locally Dickite
What is the age of formation for the Carlin-Type Deposits?
Late Eocene (39 Ma)
How was the age of the Carlin-Type Deposits determined?
Rb-Sr dating of Galkhaite.
What other deposit types were formed around the same time as the Carlin-Type deposits?
1) Au-rich Porphyry Copper Deposits
2) Skarn Deposits
3) Distal-Disseminated Deposits
What is the name of 2 Au-rich Porphyry Copper Deposits that formed near the Carlin-Type deposits around the same time?
Bingham Canyon
Copper Canyon
What is the name of 2 Skarn Deposits that formed near the Carlin-Type deposits around the same time?
Fortitude
McCoy
What is the name of 3 Distal-Disseminated Deposits that formed near the Carlin-Type deposits around the same time?
Lone Tree
Cove
Hilltop
How do Skarn Formations Form?
Generally form when carbonate rocks (limestone, dolostone, marble) are intruded by a magma body and altered by contact metamorphism and metasomatism. As the magma cools, water is expelled and travels through the carbonate rocks causing metasomatism to occur.
What are the three main trends for Carlin-Type Deposits
1) Carlin Trend
2) Battle Mountain-Eureka Trend
3) Getchell Trend
