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Jordan University lecture Gold Deposits

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Elizabeth Zbinden

on 8 October 2013

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Transcript of Jordan University lecture Gold Deposits

Disseminated Gold Deposites
HASHEMITE UNIVERSITY
Disseminated
Gold Deposites
Geological History
Metallization
(During hydrothermal system)
Carlin mine in Nevada
Faculty of Natural Resources
and Environment

Amani Abu Al-adas
Nedaa Nakhlih
Maha Mashqbeh
Rawan Batta

Dr.Khitam Zughoul
Out lines
Gold - Au
- Atomic number : 79
- Atomic mass : 196.9655 g.mol -1 -

-Electronegativity according to Pauling : 2.4
- Density : 19.3 g.cm-3 at 20°C

- Isotopes : 7
- Melting point : 1062 °C

- Boiling point : 2000 °C
- Discovered : c.a. 3000 BC
Amani
Gold Production History
world mine gold production in 2008 was 2385 tons or approximately 77
million ounces. The top 15 gold producing countriescumulativelproduced approximately 62 million ounces (81% of total global production).
Distribution of gold production in 2006.
Gold Price
This is a map of where American prospectors are finding gold in 2013.
from the chart below that official gold reserves have historically been much higher, averaging around 35,000 tons. In the 1990s, central banks began selling, with reserves hitting a 30-year low right around the time the Fed began cutting rates. Ash says that gold holdings are now at a six-year high with the current amount of gold reserves just less than 31,000 tons.
Reserves as a percent of all the gold mined has also declined, with "a far greater tonnage of gold. Since 1979, you can see the percentage of reserves to total gold has declined at a much faster pace as individuals increasingly perceived gold as a financial asset.
Gold Production History
Reserves as a percent of all the gold mined has also declined, with "a far greater tonnage of gold. Since 1979, you can see the percentage of reserves to total gold has declined at a much faster pace as individuals increasingly perceived gold as a financial asset.
Gold Price
1- Gold Deposits of the World .
2- Gold Deposite in Jordan , Location and properties.
3- Disseminated Gold Deposits.3.1 Definition.3.2 What is Carlin-type Deposits.
3.3 Location Gold mining in Nevada
3.4 Geological History , Geologic Setting.
3.5 Characteristics .
3.6 Schematic model for the development of a Carlin-type gold deposit.
3.7 Metalization .
3.8 Alteration.
3.9 Gold mining in Nevada.
Gold
Gold
Gold
Gold in Jordan
*Recent geochemical prospecting in Jordan by the Natural Resources Authority (NRA) detected anomalous gold values over the northern extremity of the Arabian-Nubian Shield in South Jordan. The best anomaly, sited over felsic volcanic rocks in Abu Khushieba area, returned gold values up to 40g/t in heavy mineral concentrations collected from stream sediments.  
Gold in Jordan
Location and properties:
The deposit area is situated 90km north-northeast of Aqaba in South Jordan. The prospect located some 4km east of the Amman-Safi-Aqaba highway in Wadi Abu Kusheiba of Wadi Araba area.
*A total of 11 boreholes were drilled by NRA in Abu Khushayba area. Six of them were drilled out of the project area following the geophysical prospecting recommendations and the surface geochemical results. One deep borehole was inclined drilling at 45° to the west to a depth of 117.5 m.
- Abu Kusheiba area:
Abu Kusheiba gold occurrence is sited within quartz porphyry and quartz feldspar porphyry volcanic rocks of the Aheimir Volcanic Suites of Wadi Araba complex
The gold mineralization is hosted in an intensely silicified linear zone up to 1m in width.
The gold rock is being identified as epithermal precious metal deposition and hosted by aplite granite with felsic composition vein (Bullen, et. al., 1996).
As a result, visible gold was detected in a number of the heavy mineral concentrates up to 40g/t. Values up to 15g/t of gold were obtained from the vein and the highly silicified weathered rock in alteration zones.
- Wadi El Hour and Wadi Sabra areas:
The two areas are located south and southeast of Abu Khushieba occurrence.
Currently, semi-detailed geochemical exploration is carrying on Wadi El Hour and Sabra.
The two areas were characterized during previous geochemical prospecting by relatively high gold anomalies.
-Reserves:
*Reserves are not yet determined.
*Further works is still required in wadi Abu Khushieba prospect area to ascertain the true surface extent of the gold anomalies and the distribution of gold in width and depth.
Disseminated deposits: a scattered distribution of generally fine-grained metal is evenlydistributed in generally low concentrations throughout large masses of rock body.
An important type of disseminated deposit is the porphyry copper deposit.
Huge, low-grade, multimillionounce disseminated gold deposits have been found in sedimentary rocks in Nevada.
Disseminated Gold Deposits comprise very fine-graind
argely sub-microscopic gold that is silty and carbonaceous dolomitic limestone.

The gold is accompanied by Silica , Pyrite and other sulfide minerals and Barite , with Arsenic , Antimony and Mercury as common trace elements .
Sedimentary rock
-hosted deposits
Distal
disseminated
deposits
Carlin-type Au
deposits
Amani
What is ‘Carlin-type deposit’?
Hosted sedimentary rocks
-Carbonate-replacement gold deposits
-Micron size ‘invisible gold.’
Carlin-type deposits generally form at lower temperatures, are commonly not spatially associated with metamorphic aureoles of coeval intrusive stocks, lack strong associations with Ag and base metals, and have isotopic compositions that suggest evolved meteoric fluids and sedimentary rocks as sources for ore-forming components.
-Today we look at the size-distribution of gold deposits in Nevada.
-Location of Carlin type deposits
Carlin trend
-Sedimentary-rock hosted
gold deposits in Nevada
We can compare the current size-distribution of gold deposits to the size-distribution of gold deposits in the Carlin Trend in 1989 . Remarkably, both sets of data appear to be described by a straight line of constant slope, at least between for deposits between about 100,000 ounces and 10 million ounces in size.
Characteristics
*Host rocks

-Fine-grained, laminated dolomatic limestone which contain some silt

-Age : Cambrian~Triassic.

*Structural setting

-High-angle, normal fault
increased host-rock permeability, creating breccias.

-overthrust belt
* The difficulty in sorting out the genesis of Carlin-type deposits is related to the complex geologic history of northern
Nevada and specific features of the deposits. For example, minerals that are part of the main ore stage (quartz, pyrite, illite, and locally dickite) are fine grained and volumetrically minor.
* orthern Nevada has undergone multiple diagenetic and hydrothermal events that produced many of the same
minerals as those associated with the Carlin-type deposits,
and these events were overprinted by or superimposed
on the main ore stage.
Maha
*We focus here on northeastern Nevada, in the vicinity of Carlin itself.

*The deposits formed between 42 and 36 Ma, following a long period of contraction and crustal thickenng of themiogeocline.

*The ages of deposits coincide with the initiation of extension in this region, but although the region contains domains of extreme extension, the gold deposits are not centered on those domains.

*The region also has been the site of lacustrine deposition before, during, and after formation of the ore deposits.

*The ore-forming fluids associated with the deposits are mildly saline, slightly acidic, and fairlyreduced.
Schematic
model for
the
development
of
a Carlin-type
gold deposit
Enigmatic Origin of Carlin-type Deposites: An Amagmatic Solution?
Conceptual models for Carlin-type deposits have narrowed to three broad classes, two of which are amagmatic: (1) surface-derived and/or basinal; (2) metamorphic (orogenic); and (3)magmatic.
Models for Carlin-type gold deposits. Left: Sketches showing conceptual models. Arrows show movement of fluid; darker shading within arrows shows where fluids deposit quartz.
Model 1 shows surface derived waters descending down normal faults to the brittleductile transition zone then returning to surface to form gold deposits.
Model 2 shows metamorphic waters rising along faults. Small arrow labeled
3 shows possible subordinate magmatic inputs to either model.
Model 3 shows magmatic-hydrothermal system related to multiple intrusions. All models have minor inputs of unevolved meteoric water (1a).
Right: Solubilities of calcite and quartz (grams/kg H2O) showing contrasting paths for siliceous replacements for models, all ending in formation of jasperoid
Rawan
-Pre-ore stage:
-Jasperoid replaced carbonate.
* Gold ore stage:
-Quarz veins and silicified breccias formed.
* Post-ore stage:
-Calcite vein formed.
-Contain barite, orpiment, reagar,
stibnite, cinnabar.
(Alteration)
*Decalcification, Decarbonization.
The earliest alteration and affects nearly all of the rocks in the vicinity of the ore bodies to varying degrees.
Most of the ores are presents in Decarbonization alteration.
*Argilic alteration.
Is confined largely to faults and fractures that served as fluid conduits and to rock immediately adjacent to those structures.
*Silicification.
Silicification ranges from weak fracture controlled boxworks to complete replacement (Jasperoid).
Paragenetic Diagram for Sulfide Ores in Sediment-hosted Disseminated gold deposits.
Intrusion-related model for Carlin type deposits
* Hypothetical zoning patterns related to an idealized Eocene magmatic-hydrothermal system
in the Great Basin physiographic province, United States.
A. Geology, emphasizing more favorable units based on higher permeability and/or reactivity.
B. Temperature and prograde flow regime, with fluids derived from a large magma chamber at depth.
C. Possible depositional environments for various deposit types, based on temperature and protolith.
D. Examples of Eocene gold deposit types.
* 1961 that the Newmont Mining Corporation found the large low-grade gold deposit at Carlin that the mining industry began to take notice .

Latitude: 40°54'42"N
Longitude: 116°19'26"W

*A gold property located about 35 km N of Carlin
* The Carlin and other mines along the trend pioneered the method of open-pit mining with cyanide heap leach recovery that is today used at large low-grade gold mines worldwide .
Nedaa
Carlin Gold mine, Elko,
Lynn District, Eureka Co.,
Nevada, USA

The Coordinates :

*Mine is a large open pit, overall 2,000 m long, 500 m wide and up to 200 m deep
*comprised of four connected pits
(West, Main, South & East)
*Estimated total production
is just under 4,000,000 Troy Oz.
65% of America's gold production is from the
famous Carlin-type gold deposits of northern Nevada.
That’s about 6.5% of the world's gold production.
About 200 million ounces of gold have been produced from
a 200 x 300 km area in northern Nevada.
This ore grades to about
0.20 to 0.25 ounces
of gold per ton of rock
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