I observed gold rims covering PGM intergrowth in direct contact with magnetite crystals on Mayak mine of Norilsk group deposits - http://www.mindat.org/loc-19033.html

Gold films over native platinum (e.g. http://www.mindat.org/photo-8357.html ,  http://www.mindat.org/photo-557285.html ) grow rather in oxide association (chromspinelides) rather then sulphides.

In this case http://www.mindat.org/photo-43350.html gold grow in equilibrium with hematite, than with magnetite.

On the locality http://www.mindat.org/loc-2766.html gold in association with selenides was detected in hematite veinlets.

Here http://www.mindat.org/photo-139035.html also gold is associated with oxides and silicates without ANY sulphide at all. Look http://www.mindat.org/photo-256525.html note intergrowth of minor gold flake with hematite crystal. The main grain is intergrown with atheneite.

I agree with your observation. In the heavy sands and fine gravel in the Zambesi River in Mozambique I find gold and PGM in a sample captured with a strong magnet, the gold content in this sample is 2033 ppm, and 173 ppm of PGM

Francesco, thanks a lot ! For my  deposit, I have found that gold occurs as small inclusion with size ranging from 100nm to 100μm, hosted by magnetite. I want to compare that to any other similar cases.

Thank you also for me, this means that to exploit the gold in heavy sediments it is necessary to crush them in more little part, hoping to free the gold contained in to the host mineral. In another case it will be necessary to use cyanide treatments to recover the gold.

Indeed, it is relatively common to find gold encapsulated in oxides and silicates without any sulphides at all. Fine grinding - normally 80% below 0.074 mm - is usually practised and is meant to speed up the kinetics of cyanidation rather than liberating gold, which would require micronization and that is not necessary.

Dear Lino, would you please offer some case that gold encapsulated in oxides. I mean gold co-precipitates or pre-precipitates with oxides, rather than occurs in the crack of magnetite.

Please refer: The Association of Gold and Magnetite (http://goldminingandprospecting.blogspot.in/2011/02/association-of-gold-and-magnetite.html)

One common type of gold deposit is one where the gold is associated with the mineral magnetite where the gold is formed in skarns of granular magnetite. The mineral has a chemical formula Fe3O4 that is often found in contact metamorphosed areas associated with intrusions of magma into carbonate or silico-carbonate rocks the intrusion itself is usually granite or monzonite-syenite. In such deposits the common minerals that are found include pyroxenes, amphiboles, garnet and lesser amounts of scapolite, vesuvianite and other silicates, but the most important is magnetite.  

Please have a look at the Geology of the Au-Cu-Bi Mine Warrego, Tennant Creek, Northern Territory, Australia. There you will find native gold mineralization in pores of the relatively massive magnetite ore including bismuthinite and chalcopyrite.

May I come back to your first question: 'Why is gold associated with sulfide minerals?'

Many sulfides play an important role as semiconductors, which have the potential to trap the gold on their crystal surfaces out of gold ion bearing fluids.  Please search for sulfides  (most important: pyrite, arsenopyrite and loellingite) as semiconductors in geological processes. I think you will find many links.

Thanks, Pedro ! I have found this association in a skarn. SInce gold is transport as sulfur complex, most of gold should relate to sulfide. Therefore, gold hosted by magnetite indicates a totally different tansport machanism in the system. 

Dear Haoyang

In the IOCG deposits, Au probably can be deposited along with magnetite. for example in the iron skarn deposits of Semnan province in Iran, gold was reported.  

Thanks alot, Ali. Would you please provide more detail about that deposit or relevant references?  

Dear all, many thanks for your kind message. We have released a study on magnetite-hosted gold. Please find more detail in our paper: Nano- to micron-scale particulate gold hosted by magnetite: a product of gold scavenging by bismuth melts: Economic Geology, v. 112, pp. 993–1010. I am looking forward to hearing from you.

We have a Magnetite- Apatite-Chalcopyrite deposit associated with a massive quartzite band next to a crustal scale thrust zone. But so far gold in any form is not recorded in the vicinity. There are historical evidence for gold mining in this area. Is there any prospects for gold?

While I don't know anything about it's occurrence in magnetite, gold sulfide Au2S and Au2S3 are fairly common. I have seen gold electrodes dissolve in sulfide melts when a grad student attempted to use it as an electrode in a molten salt battery.

I would be interested in more of the research done on the Zambezi river in Mozambique