Hello Frank
I'm not sure if you recall, but back in late 1997 I posted the following on the DML thread which was very active at the time. It should give you a geological snapshot as well as help to explain why I believe SVB has good geological potential for a significant deposit.
The read is somewhat technical but if I recall, I tried to word it so that it would be relatively easily understood.
To:Ed Pakstas who wrote (1184)
From: VAUGHN
Hello Ed
Here is the geological post I promised to bore you with.
Over the past few weeks I have been fortunate to find and read several very informative books on geology including very specific chapters on Ni:Cu:Co:PGE Sulfide deposit geology, various geological deposits and Labrador's Nain/Churchill Province geological history.
The majority of this very interesting and detailed information came from three books. The first is published by the Geological Survey of Canada (1995) entitled, Geology of Canadian Mineral Deposits. Others included the 1996 Canadian Minerals Handbook (Review And Outlook) published by Natural Resources Canada, and Petrography of Igneous and Metamorphic Rocks by Anthony R. Philpotts.
I would strongly recommend at least the first two to anyone with an interest, as they give a complete geological analysis of every major mineral deposit in Canada, parallel world deposits, production, grades, economics, geological settings and requirements for exploration for similar deposits.
Ed, while I may use geological terms from the books, I will attempt to explain their meaning as I go, so bear with me and please keep in mind that I am not a geologist so any experts out there feel free to comment please.
Firstly, there are three principal types of Ni ore found around the world, Sulfide (all Canadian producers) Lateric & Saprolitic (found exclusively in the tropics).
I will briefly touch on Lateric & Saprolitic deposits because they actually account for more known Ni ore reserves around the world than Sulfide, but are typically not as high grade and are more expensive and difficult to process. Apparently, these two deposit types are the tropically weathered remains of exposed sulfide deposits. The easily eroded Ultramafic host rock and the sulfide ore have been reduced into, often very large, but generally weakly mineralized sedimentary deposits. These typically run no more than .06% Ni with exceptions up to 1.22% Ni & .11 Co. Because the ore is bound up in weathered clay and/or iron, recoveries are difficult and expensive often running no more than 60% of grade. If you have ever tried to wash clay off your truck tires, you can readily understand how difficult it must be to process such ores.
As an aside, this past summer I attempted to screen diamond indicator mineral samples bound in clay I had taken from an NWT lake edge (marsh). It took me the better part of a day to break up the clay and reduce it with a high powered jet stream until its particles had been completely screened. Never again!
The bottom line here is that while Lateric & Saprolitic deposits account for huge reserves, they are mined economically in only a few places and in general, are typically of little threat to the economics of reasonably concentrated and/or shallow sulfide deposits.
The world's major Ni Sulfide ore deposits (generally whole camps not individual mines) are listed below. There are various ways they could be ranked, value of ore, tonnage, ore %, etc. I have attempted however to rank them by a rough ratio of their Ni:Cu ore grade and deposit size with an economic Ni cut-off of roughly .5%. A few of these camps also have very economic values for Co and/or PGE's however this data was not available for all, therefore for comparative purposes, it is excluded for rankings. However, where numbers were published, I have attempted to indicate them or at least indicate that there are economic values with a (*).
Prod/Res.
No Name (Bt) Ni% Cu% Ore % Ore (Mt) Co% PGE's
1 Sudbury 1.648 1.2 1.03 2.23 36.75 .12 10g/t
2 Noril'sk (Russia) .555 2.7 2.07 4.77 26.47 * 340g/t
3 Jinchuan (China) .515 1.06 .67 1.73 8.91
4 Voisey Bay (CDN) .150+ 3.6 2.17 5.77 8.66 .15
5 Thompson (CDN) .089 2.5 .13 2.63 2.34
6 Kambalda (Aust.) .048 3.6 .25 3.85 1.85
7 Mt. Keith (Aust.) .270 .6 .0 .6 1.62 .4
8 Deluth (USA) 4.000 .2 .66 .86 36.00
9 Dumont (Que/CDN) .150 .5 .0 .5 .75
10 Bowden (Man/CDN) .080 .6 .0 .6 .48
11 Selchi (Botswanna) .0494 1.04 1.12 2.16 .11 * *
12 Agnew (Aust.) .0465 2.08 .1 2.18 .10
13 Raglan (Que/CDN) .0185 3.13 .88 4.01 .07 .05 *
Three points to note from the above chart:
1. VB is a significant world class high grade (1/3 open pitable) deposit,
2. In general, in sulfide deposits, where Ni:Cu ore ratios run approximately 1:1 there is a higher incidence of economic grades of Co and PGE's. This is especially true when Cu grades are elevated which will be more evident in some of the comparisons that follow, and
3. While it is insanely preliminary, as you can see, that the Donner/Northern Abitibi 11.75% Ni : 9.7% Cu : .43% Co grades are better than those found in most of the camps around the world.
Now just a bit of geology Ed and only because its important for the point I want to make at the conclusion of all this.
Sulfide Ni ore deposits come in four different and specific geological settings or types, but are always associated with what is called Ultramafic rock (90%> Olivine, composed chiefly of ferromagnesium minerals, orthopyroxene, clinopyroxene, and hornblend). The % of magnesium is important as you will see later, but simply put, the higher the % of magnesium, generally, the higher the % or grade of Ni. There are various types of Ultramafic rocks and differentiating them, to put it in contemporary terms, is a very anal exercise. They can be Alkaline or Subalkaline, silica rich or poor, intruded or extruded, etc. etc. For our purposes Ed, I am going to keep it simple, so by and large, they are differentiated by various combinations of other minerals. How's that?
Ni Sulfide Ore Deposit Types
1. Astrobleme - An Ultramafic intrusion into the shattered (brecciated) remains of an asteroid impact crater. The only known incidence of this type of deposit is the Sudbury camp in Ontario.
Coincidentally, there is a 28km wide asteroid impact crater within a few hundred kilometers of the SVB site, but I do not believe it is close enough to have contributed to the deposit. see -
gdcinfo.agg.nrcan.gc.ca. and
gdcinfo.agg.nrcan.gc.ca
2. Rift/Continental Flood Basalt - Think of a sealed tear or "rift" in the earth's crust and a bubble or belch if you prefer, of Ultramafic rock flooding into it. In effect, like you blowing a bubble with chewing gum. The most well known pure example of this is the Russian Noril'sk deposit although the South African Bushveld Complex deposit is apparently a unique variation. Both are of course, the largest and most PGE rich deposits in the world.
As an aside, it has been theorized that the Darnley Bay anomaly near Paulatuk may be another example of this, but that is another story.
3. Komatiitic - Again, in simplistic terms, this is the equivalent of the #2 "Rift/Continental Flood Basalt" bursting out onto the earth's crust. Your chewing gum bubble popping! It occurs almost exclusively on Archean (very old) terrains and is the volcanic equivalent of Peridotite. Peridotite is the rock considered to make up most of the earth's deep mantle and is where most diamonds are formed. The most well known type of Peridotite is of course Kimberlite, the transporting rock of diamonds.
Komatiitic Ultramafic lavas tend to have very high magnesium (MgO %) contents and some associated deposits in Langmuir, Ontario(48.5% MgO), Thompson, Manitoba (44% MgO) and Kampalda, Australia (43% MgO) have amongst the highest Ni grades found anywhere in the world, (16%,14% & 13% respectively).
4. Tholeiitic - Again, in simplistic terms, this is an Ultramafic intrusion which is classified as Subalkaline primarily by virtue of having a SiO2 (silica or quartz) content greater than 46%. There are other mineral content factors but this is the principal reason. Tholeiitic basalts can be subdivided again into various categories by virtue of characteristic mineral content percentages, one of which I find particularly intriguing. Tholeiitic Picrite which has a MgO (Magnesium) % of 20.8.
If you haven't guessed, Voisey Bay is a Tholeiitic Ni deposit, one of a very few in the world and the Leopard Troctolite is the Tholeiitic Ultramafic ore.
Typically, Tholeiitic Ni deposits have not proven to be particularly rich ore bodies probably due to one of two factors, either their host Tholeiitic rocks have not been particularly rich in MgO hence Ni, and/or the necessary Sulfides may not have been present in sufficient quantities to provide the necessary conditions for Ni:Cu to precipitate out of their intruding fluids.
However, for the SVB play, this is where things get very interesting geologically.
Apparently, the Sulfides are not present in any Ultramafic intrusion. The Ni, Cu, Co and PGE's are all there but unless the host rock has a high Sulfide content, the chemical conditions will not exist to facilitate the precipitation of the ores out of their fluids.
The Churchill Province rocks which may have the greatest sulfide content are probably the metasediments, orthogneiss and migmatites that underly the gabro, norite and troctolite Nain Province rocks. Any gneiss metamorphosed from the aforementioned probably also contains the necessary sulfides.
The only remaining factors should have been the right temperatures and pressures necessary to facilitate the chemical reaction and precipitate out the ore and of course the physical setting to trap the precipitating ore fluids.
According to a geologist (with a major mining company) who I met over lunch at the NWT Geoscience Forum Wednesday (who's training and experience lies in Ni:Cu sulfide ore deposits), what makes the VB Ovoid Zone so unique, is the bowl like shape to its basement gneiss's and metasediments. They provided the sulfides and literally cupped and held the precipitated ore fluids while they accumulated.
Therefore, assuming that such pockets, bowls and faults exist in SVB, we have all the conditions for the accumulation of large and probably multiple massive sulfide deposits.
Now, I discussed the geological setting with that geologist mentioned above, and the grades that hole 97-75 kicked out, and while he agreed it was entirely possible to have higher grade stringers within a lower grade deposit, it was unusual, especially to have such high grades in a Tholeiitic deposit.
I asked him the following what ifs?
1. What if the troctolite was in fact a Tholeiitic Picrite, MgO = 20.8%?
Remember the higher the MgO the higher the grade of Ni in ore. Entirely possible he said, but he didn't think that would account for the 9.7% Cu as MgO doesn't effect its concentration to such a degree. I pointed out that despite the high Cu% no significant PGE's had been reported from the assays. While he said it was not unusual for Tholeiitic deposits to have low or no PEG values, it was unusual to have such high Cu grades without PGE's.
2. I asked, as PGE's are amongst the heaviest elements on the element charts would they not be more likely to be found towards the bottom of any deposit? To which he replied that that was fairly typical, and that is where they tend to be found in Sudbury, Noril'sk and the Bushveld Complex in SA.
3. Finally, I asked that if the grade was so unusual (high) for a Tholeiitic deposit, would it be possible for there to have been some secondary remobilizing mechanism perhaps a Rift/Continental Flood Basalt intrusion or some other volcanic event, to which he replied that that seemed the most likely explanation for such high grades given the limited information presented.
So there you have it.
Some very interesting possibilities. Now if Teck can just find that bowl or fault...pots & pans!
Here are just a few more geological tid bits.
PGE Host Rock Definitive Characteristics
1. Located within large Ultramafic intrusions of Tholeiitic affinity
2. Presence of micria hydrous silicates
3. Accompanied by minor sulfide with recoverable Ni:Cu or Chromite
4. Pegmatic textures within largely cumulate rocks.
Sulfide minerals associated with Dunite and Peridotite have higher Ni to Cu ratios than those associated with gabro and norite. (VB & SVB)
Ni - World consumption - 936,000 t in 1997
- World production - 958,600 t in 1997
- Canadian production - 197,000 t in 1997
- Canadian production - 340,000 t by 2005
- World consumption - expected to increase at an average of 2% per year.
- Russia = 24.1% of world mine production
- Canada = 17.8% of world mine production
Co - World production - 30,280 t in 1997
- Canadian production - 4,181 t in 1997
- Canadian production - 7,400 t by 2000
- World production exceeds consumption but expected to be = by 2000
Cu - World consumption - 12,213,000 t in 1996
- World mining production - 10,676,000 t in 1996
- World refined production - 12,438,000 t in 1996
Inco - 188,000 t/y Ni in 1996
- 688,000 t/y Cu in 1996
- 1,534 t/y Co in 1996
VB - 123,000 t/y Ni in 2001
- 91,000 t/y Cu in 2001
- 3,200 t/y Co in 2001
AVERAGE ANNUAL PRICES
Name Unit 1991 1992 1993 1994 1995 1996
Co $/lb 11.0 24.3 18.0 19.9 27.069 27.5
Ni $/lb 3.80 3.18 2.43 2.92 3.90 3.50
Cu $/lb 1.08 1.03 .85 1.07 1.35 1.06
Pt $/oz 376.08 359.80 374.03 405.00 424.35 397.17
Pd $/oz 88.89 88.23 122.35 142.63 151.23 128.08
Rhm $/oz 3,739 2,365 1,066 712.68 424.15 280.72
Its 4:50 am and I need some sleep, I almost lost this file. Sorry it didn't import into SI better. Tried that txt and Fixed Font routine but it doesn't seem to work for me.
Regards
Vaughn |
