Vein deposits have the best gold, but the predictability of gold content within the vein is highly variable. Alluvial gold on the other hand is less variable in parts per million (ppm) within sedimentary deposits, but is disseminated widely through the strata and of low ppm content. The problem is finding the best veins for working. That is a problem!

regards

George Strachan

Dear Prof. George

Many thanks for your excellent answer to my question about Au deposits.

Best in what sense? In my view the "best" gold deposit is the one that has the highest rate of return on investment. Geology does factor into that, but many other non-geological factor do too.

Dear Gholamreza Fotoohi Rad ,

You got a good answer from George J. Strachan , : 'Vein deposits have the best gold, but the predictability of gold content within the vein is highly variable.'

the following questions should be asked in this regard:

What types of veins does gold appear in? What is the main thing that leads to the fact that these veins can be rich in gold?

Are there any other types of gold deposits that are related to veined-type gold?

...

Here is pretty good writing, read it.

Article New occurrences of tellurides and argyrodite in Rosia Montan...

I wrote my state thesis in the neighborhood of this environment. (Zlatna Basine) in relation to Paleogene Volcanism. I probably solved the volcanic tectogenesis of this area in my head this year... I haven't been able to answer a specific question for more than 10 years.

This solution seems to be of great importance!

It should be nice to test it but I would like to be present personally at the testing.

Regards,

Laszlo

Veins are the source of best gold deposit but content of Au in vein is highly unpredictable

Thinking about it - while vein deposits may be the richest primary source of gold, placer deposits or alluvial deposits could be the best source of gold in the sense that through weathering process, the primary source releases the gold, which then gets concentrated by action of water into alluvial/placer gold deposits. Even disseminated type of deposits can be concentrated into rich alluvial/placer deposits through this process. Recovery of gold nuggets weighing hundreds of grams have been reported in many alluvial/placer deposits. Additionally, alluvial deposits are easier to work than primary vein deposits to recover the gold. Most artisanal gold miners work the these alluvial/placer deposit types.

Dear professor

Many thanks for your excellent answer to my question.

Gold-bearing porphyry deposits can be very large, although low grade.

Elias has given a very clear answer. The Cononish gold mine in Scotland was opened fairly recently. - one day its reserves are estimated as really substantial, the next day the vein has nearly run out along with its gold. Variability of gold content in veins is one issue, the other issue is that it entails hard rock mining. My cousin in northern Canada opened such a mine , but unfortunately his partner in the venture was killed in an explosion in it.

Alluvial gold is often found in soft sediments and easy to extract gold from. The mining company always has to balance winnable Au reserves against the cost of mining and global market prices at any one time. Rich reserves may prove less economic, if remote, hard to mine and better to hold in reserve until gold prices rise.

Kind regards

George

1)Magmatic gold deposits

1)Volcanicmassive sulfide deposits (VMS)

(1)Kuroko-type

(2)Besshi-type and Ural-type

(3)Cyprus-type

(4)Iberian-type

(5)Greenstone-Belt-type

(6)VMS deposits of unknown type in medium to high grade metamorphic terrains

2)Listwanite-type Au deposits related to ultramafic igneous rocks

3)Gold deposits associated with felsic intrusions—igneous rocks (IRG-systems)

4)Porphyry Cu-Mo-Au deposits including co-magmatic breccia pipes

(1)Calcalkaline porphyry Cu-Au-Mo deposits and Cu-(Mo) breccia pipes

(2)Alkalic porphyry Cu-Au/ diorite porphyry copper

5)Pyrometasomatic Au skarn deposits

6)Shallow high- and low-sulfidation Cu-Au-Ag deposits

1)High sulphidation-type/ quartz alunite-type Au-Ag-Cu deposits

2)Low sulphidation-type/ adularia-type Au-Ag deposits

3)Hot spring Au deposits bound to subaerial siliceous sinter

7)Mn-Au-Ag-Fe-Ba-F low-sulfidation deposits

8)Alkaline igneous rock-relatedAu-Ag-Te deposits

9)Carbonate-hosted disseminatedAu-Ag deposits(Carlin-type)

10)Cu-P-REE-U-Th-(Au –PGE) vermiculite deposits

2)Structure-related gold deposits

1)Orogenic gold deposits

2)Iron oxide breccias with Cu-Au-Ag-U deposits

3)Sedimentary gold deposits

1)Laterite-saproliteAu-(PGE-Sn)-Fe-Al-Mn deposits

2)Au-PGE placer deposits

3)Buried (Paleo) Au-U-(PGE-Th) placers (quartz pebble conglomerate)

4)Au-bearing banded iron formation

5)Au-bearing black shales

6)Au-bearing coal

4)Metamorphic gold deposits

1) Metamorphic Au-As-Pd-Hg-Bi-Te mobilizates

All of these Au deposits can be looked for in the field and exploited for a profit. It only depends on the area where you are in search of them. In a strongly metamorphosed terrain it makes no sense to try and find a Carlin-type Au deposit. As such it is not possible to make any ranking although porphyr coppers, orogenic gold deposits, epithermal Au deposits of different degree of sulphidation and VMS deposits rank very high.

HGD

Greetings to all teachers

In my opinion, Orogenic Gold Deposits are the best reserves in the world, both in terms of reserves, in terms of grade and in terms of gold production. These deposits are mostly unknown and have been exploited less than vein deposits in the past. My experience of 10 years in the exploration of this type of deposits in the Sanandaj-Sirjan structural zone in West of Iran has not shown any evidence of old mining.

Your contributors outlined the great variability of gold deposits and the plethora of conditions that can become "the best".

I am amazed at those prospectors scouring Australia (and shown in videos on Discovery channel) looking for nuggets and some of them can be very big. Anyone who can walk can find them with the help of those expensive metal detectors.

During my time at an Abitibi gold mine (while the price of gold was only 100$) the manager begged me to look over all mine data to find any missing targets. By looking at sampling results of the walls of all tunnels I discovered what appeared to be a high grade vein. After washing the walls it turned out to be a stratiform chert horizon with plenty of pyrite and calcite. The only academic to study it, Prof. Rob Kerrich, described it as volcanic in origin and deposited along with greywackes of the Pontiac Group.

We traced this deposit for at least 1600 m with no end in site. This year a mine developer used it to make an underground ramp (in ore), some 5 km away to access another gold deposit.

In a mine report I concluded that this stratiform deposit was probably the source of all the gold in that mine (total production is over 100 tons, but it is still producing).

In that particular situation this deposit was "the best".