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EducationWhat constitutes an ore?

18th Mar 2019 07:16 UTCThomas Farley

Hello. More rookie questions, this time about what constitutes an ore.

I read somewhat universally that an ore is “a naturally occurring solid material from which a metal or valuable mineral can be profitably extracted.” To illustrate that, perhaps, I have read such things as “chalcopyrite is the most important ore of copper.” But what if that mineral, like chalcopyrite, is in quartz along with other minerals? Those other minerals perhaps being of greater value than the copper?

For example, I have a quartz slab that XRF analysis says contains copper at approximately 35,000 PPM. A geology professor who worked for two years at a copper mine also looked at the slab and pronounced the copper material as chalcopyrite. Okay, is this rock a copper ore specimen or simply quartz that contains copper? When we say ore, do we mean a mineral by itself or do we include it with its matrix? Or is that the right question? If not, what is the right question?

To confuse matters, the XRF analysis also reveals gold as 81 ppm and silver at 140 ppm. Assuming those values are correct, and I know everyone would prefer a fire assay, do these more economic materials change our perspective of the rock? That is, do we now have gold ore or silver ore? Or all three? And the rock has rhodium, too, at 42 ppm. So, what do we have? I am now thinking of calling this specimen as quartz with copper, gold and silver in matrix, skipping any mention of ore. I assume, too, that I can say those minerals exist by way of testing, even if the gold, silver, and rhodium are not viewable at the macro level. What do you all think?

BTW, I have tried looking up this problem off the net. I have on my shelves a copy of that boat anchor, A Dictionary of Mining, Mineral, and Related Terms, written by Paul Thrush and the Staff of the Bureau of Mines. It weighs eight pounds and is over 1,200 pages. With at least six definitions of ore. Thanks in advance, I really don’t know enough to ask the right questions. Which is why I am here.

18th Mar 2019 07:24 UTCAlfredo Petrov Manager

Well, you can't open a mine in a single specimen, so whether it qualifies as "ore" or not would depend on how many millions of tons of it there is at the locality where it was found. ;))

Specimens are usually highgraded and do not represent the average material in a mineral deposit, so it's impossible to judge ore value by studying a specimen. You need systematic sampling.

18th Mar 2019 08:07 UTCThomas Farley

Thanks for your reply. I think you may be referring to an ore deposit which I do understand. To clarify, I am not thinking of opening a mine, rather, I am working on a book that explains basic principles to new rockhounds and prospectors. Small scale miners, perhaps, but mostly for people looking for specimens and trying to understand same. As such, I am only trying to work out definitions based on some rocks that I have self-collected or acquired during my time of prospecting for gold. I find the definitions for ore confusing and that's why I asked for help.

To add to the discussion, us gold hounds used to use the term free milling gold for quartz that contained that metal and nothing else. The kind that only mechanical means were needed to liberate the gold from its matrix. The other kind that I described previously, is what we would call a complex ore, something requiring mechanical and chemical means. To make this post perhaps more interesting, I have attached a photo of a slab that I am describing. I believe the black material is an iron sulphide. Thanks, Tom

18th Mar 2019 08:31 UTCLuca Baralis Expert

"ore" is a word better used in economics than mineralogy or geology.

A rock massif / layer become "ore" only when someone can make profit from it.

Because it happen there must be at least 1) enough interesting minerals (interesting here means that it has a market; if precious "enough" can be as low as ppm - parts per million, nevertheless you need tons of raw rock), 2) the interesting mineral/minerals should be easy (possible and not too expensive) to recover, 3) the deposit must be in an easily accessible place (to take there machinery, people and to take away your digged ore), 4) as you probably have to invest a lot of money, you need also long lasting work permits, that is you need political and economical stability...

As told, it's mainly a question of $$$!

However "ore" is often used to say that some mineral is frequently used to extract some chemical or material:

chalcopyrite is an ore for copper, galena for lead and sometimes for silver, hematite for iron,... marl could be an ore by itself for cement making.

18th Mar 2019 10:06 UTCFranz Bernhard Expert

>>“chalcopyrite is the most important ore of copper.”<<

That´s true, but it would be more clear to use the term "ore mineral" instead of "ore" for chalkopyrite. Same for galena etc.

Your specimen could be an "ore specimen" ("chalcopyrite in quartz gangue with Au- and Ag-contents"), if all the criteria listed by Luca are satisfied. In itself, it is chalcopyrite in quartz.

As already pointed out, the definition of ore is an economic one.

>>marl could be an ore by itself for cement making.<<

Oh yes! That´s not the traditional view of marl, but I see also marl as an ore of cement (if it can the mined profitably!). But thats largely semantics, and yes, there are many definitions of ore.

Franz Bernhard

18th Mar 2019 10:08 UTCBen Grguric Expert

In an actual mining scenario what constitutes ore is this. Assume you have a tonne of material from a copper mine containing chalcopyrite and assaying 1% copper. Let the copper price be US$6500 per tonne. You are not making elemental copper but chalcopyrite concentrate assaying 28% Cu. For this you only get 60% of the LME copper price ($3900)

That tonne of material contains $39 worth of copper, but in your processing you only recover 85% of the copper in the rock (leaves you $33.15).

After processing costs ($20 per tonne) and mining costs ($12 per tonne) are deducted you are left with a profit of $1.15. That tonne is therefore technically ore as you are making a profit by mining and processing it.

18th Mar 2019 10:09 UTCKeith Compton 🌟 Manager

Thomas

Perhaps you should explain your project more. I believe that you are writing a book on rockhounding and prospecting in the Southwest (USA) for "Adventure Publications"? Yet you indicate that you are "working on a book that explains basic principles to new rockhounds and prospectors".

So, basic principles of what - collecting, mining (or finding a mining deposit) or simply looking for rocks?

If you Google "mineral ore" you will get, courtesty of "Wiki":

"An ore is an occurrence of rock or sediment that contains sufficient minerals with economically important elements, typically metals, that can be economically extracted from the deposit."

The Mindat glossary also defines ore as "A general term for a rock/mineral containing an economic quantity of extractable metals or other elements."

You need to determine your target audience in order to set the tone/information you want to convey.

You could get carried away with "ores".

The Olympic Dam in South Australia for example, has huge iron - copper sulphide ores: - pyrite / chalcopyrite / bornite/ chalcocite / gold, yet it also mines uranium ore as a by-product - contributing 20% of mine revenue (yet making it the second largest uranium-producing mine in the world).

Anyway I digressed, but it would be helpful to identify your target audience to determine the level of info required.

Good luck with your project.

18th Mar 2019 14:28 UTCThomas Farley

Thank you, everybody, for your comments, they are most helpful. I am still reading through them. My target audience are beginning prospectors, rockhounds, gem, and mineral collectors. A treatment of ore or ores may never get into the book, but, like other words and phrases, I need to understand them before I can decide on using them. This is all part of reading, writing and research. Again, thanks for the fine discussion. Tom

18th Mar 2019 14:37 UTCAlex Homenuke 🌟 Expert

In the modern context, the term "ore" should include "legally" as well as "economically" extracted. The technical aspects of proving that an ore deposit exists are often simpler than the social, environmental, and political hurdles that have to be overcome.

18th Mar 2019 17:20 UTCHolger Hartmaier 🌟

Hi Thomas,

Another reference worth checking out is "Prospecting in Canada", by A.H. Lang. Although published by the Canadian government as a guide for prospectors working in Canada, most of the book covers basic geology, exploration and sampling techniques, etc. that would be of general interest to the audience you are targeting. It is interesting to note that this reference spends very little time covering the topic of "ore" as such, since it is something that needs to be defined by someone with professional credentials. Since the famous Bre-X scandal, mining companies listed on Canadian exchanges are now required to file reports on their properties that are compliant with National Instrument 43-101 standards, which includes standards for the definition of how ore grades and tonnage must be reported. Prospective investors should note however that just because a mining company has produced a 43-101 compliant report, it doesn't mean that the prospective mine will be economic.

Here is the Wikipedia link that gives an overview of that legislation, as well as how it relates to other international regulations:

https://en.wikipedia.org/wiki/National_Instrument_43-101

With regard to your original post, any rock sample would consist of potentially valuable "ore" minerals and "waste" rock. Some ores are a mixture of various valuable minerals. Some are a mixture or a fine-grained aggregate of valuable minerals ("ore minerals") and worthless minerals (also called "gangue") which must be separated from the valuable minerals by processing (crushing, grinding, concentrating, smelting). The presence of trace amounts of other elements, such as gold or silver may increase the value of the ore, as they are extracted as a by-product. Other elements may introduce a complication in the processing and refining of the ore, which may render the orebody uneconomic.

Good luck!

Holger

18th Mar 2019 18:50 UTCDoug Daniels

In regards to an ore deposit, you not only have to determine if there is enough value to extract it (a whole can of worms), but you need to factor in environmental investigations before you can even start extracting - whether a large scale operation, or a little bitty one (at least, in the U.S.).

18th Mar 2019 19:31 UTCSusan Robinson

We attended a presentation on the Flambeau mine, Ladysmith, Wisconsin, years ago (this is the mine that produced the fabulous chalcocite crystals). The company that mined that deposit was Kennecott, and the geologist said it took 22 years of negotiations to finally open the mine. After the mine closed, and the pit was re-filled with the mine waste, there is a 40-year onus on the mining company if the Flambeau river, which is very near the pit, gets contaminated from the past mining activity. If you drive by the area where the mine used to be, it would be difficult to determine if there was ever a mine there. I thought I'd add this info to the conversation, since the mining laws in the U.S. have become very complicated.

18th Mar 2019 20:10 UTCThomas Farley

At the risk of crowding the message board, again, I wish to step in once more to publicly thank everybody for their comments. I do appreciate the time everybody is taking to type up their thoughts. Once again, thanks. Thomas

18th Mar 2019 20:25 UTCKevin Conroy Manager

Hi Thomas,

I don't know if you've run across the following but it's worth a read: https://en.wikipedia.org/wiki/Mining

Note that in the "Mine development and life cycle" they kind of glaze over the milling and infrastructure costs. Depending on what and where the potential ore deposit is this can be substantial!

18th Mar 2019 21:47 UTCGregg Little 🌟

Thomas;

Might the solution to your approach be to talk about the ore in the past tense. It is likely that the deposit, in its present condition, understanding and economic environment will have had anything of commercial value sent to the crusher.

In other words, rather than trying to identify or quantify a particular piece of rock as ore, talk about the mineralogy and rocks that are associated with the ore and that are responsible for the economic minerals to occur there. Such terminology like gossan, gangue, country rock, host rock, waste rock, overburden, etc. come to mind. These rocks that are often seen in mine dumps represent the geological setting for the economics. Likely the most familiar is quartz veining to host the ore, gem or crystal, but there are other hosts like massive sulphides, Mississippi Valley type carbonates, pegmatites, placers, etc. Whether your reader is a beginning prospector, rock-hound or gem and mineral collector, approaching the prospect by a geological (depositional) angle may be more valuable or productive to the enthusiast than trying to stumble, without context, on the prize itself.

Often economic deposits are happened upon by the indicator minerals and geological setting. After the ore is extracted that is largely all that is left.

Cheers and good luck

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