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#26

Zengeo
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From: Aroundabout, WA
Joined: 28 April 2017
Posts: 45
Member
18 September 2018 10:59 pm

Ben,

You look into this at all? What was the result?

The rule of thumb for large U/G mines is they become profitable over about 5 g/t.
A small show mined by a couple of guys would want higher grades because you don't have economies of scale on your side but anything from about 1/2 Oz up (roughly 15 g/t) should make good money. It'll be hard work though and cost a fair whack up front. If the orebody reaches surface, it's cheaper to dig down on it (open pit) even though you're moving a lot more tonnes of waste to get at the ore.

Give us an update anyway and if you want a Geo's opinion, feel free to PM me thumbsup

All the best,
Zengeo


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#27

goldierocks
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Joined: 10 January 2015
Posts: 1,268
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19 September 2018 10:16 am

Asking how many grams per tonne are needed to make a profit is a bit like asking how many dresses you need to have for a dress shop make a profit. The gold grade is only one of the relevant variables involved (e.g. with dresses, have you ever sold dresses or run a shop, what do you pay in rent, is it in Woop Woop north or central Melbourne, are the dresses unfashionable, how many staff are you paying, what did it cost to get your stock)?

With gold it is things like - what is the average grade (a high assay in some samples probably doesn't indicate average grade), how representatively was it sampled, is the sampling affected by "nugget effect" because the gold is coarse, can you legally peg it, will you be allowed to mine it, how wide is the vein, does the high gold extend one metre along the vein and only one metre deep (or a couple of hundreds times that as is most economic mines), what will it cost per tonne to mine it, how many tonnes of economic ore are present, what will it cost per tonne to treat it, is the ore complex (eg high in arsenic, fine gold locked in sulphide minerals), is it coarse gold that requires only water-gravity separation or will you need cyanide, is it in hard quartz with high crushing costs?

The lowest grade gold-only mine in the world averages about 0.39 g/t but is huge (immense tonnage - more than half a billion tonnes), next to a highway etc etc. Many large open cut gold mines (tens to a few millions of tonnes of ore) operate at 1-2 g/t, underground mines (one to a few millions of tonnes) at 4-8 g/t, narrow-vein underground (eg hundreds of thousands to many tens of thousands of tonnes) at more than 9 g/t. A single miner with his own show and a quartz vein only tens of centimetres wide that he can only produce small tonnages from each year ( say a couple of hundred tonnes) and which needs long road transport and cyanide treatment commonly needs 20-90 g/t or more. But these are nothing more than ball-park figures.

Gold mining is a business like any other, and requires good business sense and good advice (which costs). Not something anyone starting fresh is going to get rich on unless they have stumbled on a vein with gold like fruit in a plum-pudding. One should not confuse recreation and business otherwise.


Robert Benchley...
I have kleptomania, but when it gets bad, I take something for it.

6 users like this post: RM Outback, Dron, Zengeo, Prospector B, Swinging & digging, Matt80

#28

OldGT
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Joined: 10 May 2017
Posts: 540
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19 September 2018 09:45 pm

I'm unsure if it's helpful but I'll retell an account relayed to me by a member of a small mining family of one of his dad's prospects.

A mid size mining company took out an EL over land worked from the late 1800s, with numerous shafts that were well worked. Rock chip samples were taken in the early 1980s which lead to further testing. Eventually drill samples were taken and assayed. Some high readings at surfaced depths to 30m had varying g/t from 3 to 56. The company began to face some financial difficulties and had decided to relinquish some of its more remoTe prospects which included this EL.

Along came company B who proposed to do some smaller scale open pit but concluded profitability of mining with machines and temporary workforce was likely a smaller return than was justified and so held the land for a couple of years before focusing on current operations.

One of the original drillers had semi retired and decided to move to the area with his young teen boys. He had knowledge of the original drill results and decided to do some small scale work, it was the late 80s and small scale operations were quite lenient in restrictions. They sunk two shafts and managed with small rudimentary machines and after hours labour between 3 people to extract over 20 ounces. The cost of operations for extraction, processing was around $40000(then) and work completed over 3 years, quite a tidy return.

A small mining company took over the operation, worked a smaller open pit and lost quite a bit of money in less than 6 months of operation. They skipped rehab and the company went bust. The land today still sits almost as it was in the early 90s. Moral of the story here is great assays can mean a win or a loss, as can the approach which is exactly why goldierocks is spot on in his assessment.

As an aside there was no average material lifted from those shafts that would indicate 56g/t was near accurate.

To this day that same family still does serious prospecting often for profit.

Last edited by OldGT (19 September 2018 09:59 pm)

1 user likes this post: Zengeo

#29

Zengeo
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From: Aroundabout, WA
Joined: 28 April 2017
Posts: 45
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19 September 2018 11:32 pm

Oh yeah. Many a man has lost a pot of gold chasing gold.

Ben just asked for general rule, so I gave him one. Then a bit more info on the subject of grade.
If a solid bunch of assays don't come back with high enough grade, don't even think about it.
In high grade narrow vein orebodies the distribution of gold is typically 'nuggetty', not meaning there are nuggets everywhere, a term meaning you could take two samples right next to each other and one will come back at 50g/t. Woo hoo! But the one right next door comes back at 2g/t. Bugger. Hence the average of grades. (There's a lot else to do on that point but too much to go in to) And as Goldielocks pointed out, there's a hell of a lot more to it than just grade.

The devil's in the detail and there are a lot of moving parts, as well as a lot of other sayings I'm sure.
You need to be totally on top of all of it and have solid confidence in your numbers, on paper, before you even think about actually mining.

But it can be done. Rios is doing it thumbsup


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#30

Zengeo
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From: Aroundabout, WA
Joined: 28 April 2017
Posts: 45
Member
19 September 2018 11:42 pm

OldGT wrote:

They sunk two shafts and managed with small rudimentary machines and after hours labour between 3 people to extract over 20 ounces. The cost of operations for extraction, processing was around $40000(then) and work completed over 3 years, quite a tidy return.

20 ounces at about $400/Oz at that time wouldn't have gone too far.
You mean 2,000 or 20,000 Oz?


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#31

OldGT
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Joined: 10 May 2017
Posts: 540
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20 September 2018 08:06 pm

My bad mate, typo in edit. 200oz. About 90k worth. Not bad for a Dad & 2 teenage sons part time. And in rereading to clarify they had most of the equipment needed, what I was demonstrating in the retelling was from scratch the mining operations cost was 40k if you started from scratch.

Probably best I keep my comments to simple sentences and emojis after 16 days straight working haha.

#32

Eski
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Joined: 10 May 2015
Posts: 178
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21 September 2018 07:43 pm

Never had a mine , but read somewhere that the efficient extraction , movement and processing of ore can make or break it. I think Steven Barnham in one of his books mentioned the red hill (or big Hill) mine. the ore moved by gravity to a crusher that was water driven and then a sluice. a kid watching the crusher/box , then really all the hard work is on the face.

all mines are different but i think efficiency is key, then balancing that with AFFORDABLE capital investment to build this Efficient Machine.

Wish i had a mine........

#33

Harlequin
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Joined: 26 October 2013
Posts: 21
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08 March 2019 11:46 am

Ben, I presume the host rock is quartz as you mention an outcrop nearby. The comments so far are correct and what it comes down to is small versus big time mining. The big miners will pay up to $1,000 per ounce to recover the gold but they won't even start unless they have a proven deposit which will allow them to treat around 4,000 tonnes a day for , say, 20 years. So the question is can you make a profit with limited funds and resources. That is working with low grades. The different grades range from .01 to 17.71 which is a mixed bag with .01 being what is in most rocks to 17.71 which is really exciting if that grade is consistently in huge tonnage. I'm prospecting an area of around 30 sq km hoping to find an ore body of quartzite following an assay of 2.3g/t. We know the gold is there but we have to prove there is enough to justify a mine. If you are going to go ahead you have to weigh the heartbreak of dealing with Government, spending, spending, working with material of 7 hardness, against the deep joy and satisfaction of mining for gold - whether you're successful or not. If you aim at nothing, you'll always hit it ! Perhaps you could spend some time getting a quantity of rock to work with then crushing it (dolly pot and Cobra rusher?) then do the maths. I wish you all the best!
,

#34

goldtrapper
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Joined: 26 September 2018
Posts: 273
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08 March 2019 01:40 pm

If you take the photo's with your phone make sure gps location is turned off! Otherwise you will have the place invaded. Also don;t give out anymore details about mine/report dates sample dates etc a a slueth could work with that info and narrow down your location......... just saying.

1 user likes this post: goody2shoes

#35

goldierocks
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Joined: 10 January 2015
Posts: 1,268
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08 March 2019 06:26 pm

Victorian quartz vein gold. A vein that averaged only 2 or 3 g/t and was only a few metres wide would not be economic. Most vein deposits of that size (large ones - say a couple of million tonnes of quartz ore) need around 5 to 9 g/t to be economic. In places like Bendigo the economic veins that size were usually 12 to 20 g/t. For a small miner with a vein only tens of cm wide you would probably need 90 g/t or similar to really make any money, but at 20 g/t plus it might be a hobby mine. However large volumes of ore tens of metres wide (many tens of millions of tonnes of ore) that can be open cut at surface, it might be economic at 1.5 to 2.5 g/t. The lowest grade mine I know is in Alaska ("Fort Knox") and averages 0.38 g/t gold - but it is hundreds of millions of tonnes. To get an idea what that looks like, a cubic metre of rock has a mass of around 2 to 3 tonnes.....

And as many people have said, that is all just a ball=park indication (so many things affect economics). And to average 5 g/t you would expect to see many assay values of 10 to 20 g/t.

These figures are based on actual mines being worked.


Robert Benchley...
I have kleptomania, but when it gets bad, I take something for it.

2 users like this post: RM Outback, jethro

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