Silicon Investor (SI) -- The First Internet Community

STOCKTALK

We've detected that you're using an ad content blocking browser plug-in or feature. Ads provide a critical source of revenue to the continued operation of Silicon Investor. We ask that you disable ad blocking while on Silicon Investor in the best interests of our community. If you are not using an ad blocker but are still receiving this message, make sure your browser's tracking protection is set to the 'standard' level.

Strategies & Market Trends : Ride the Tiger with CD -- Ignore unavailable to you. Want to Upgrade?

To: koan who wrote (94365)	10/6/2007 2:28:27 PM
From: E. Charters	Read Replies (1) \| Respond to of 313046

It is a fact that dynamite as a method of comminution is cheaper than mechanical crushing by three times. Since powder is 5 times more expensive by energy unit than electricity applied to mechanical force, it follows that blasting is fifteen times more efficient at breakage than mechanically applied force. It is believed this is because blasting force exploits tensile force against rock more than impingement does. When rock is squeezed a certain percentage is compressive, and a certain percentage is tensile stress due to elongation strain. In crushing, compression dominates perhaps partly because of confinement. You would think it would not be hard to be more efficient than crushing, as it is the single least efficient industrial operation there is, working at around 0.5 to 1.5% efficiency. It is hard however to figure a way to break rock to very fine sizes by any other method. However to the degree that it is practical vis a vis scattering losses, the more finely you break by dynamite, the less size reduction costs will be. That is partly because rock is micro fractured intensely by high energy high brisance explosives which assists further comminutative breakdown. You may save as well in not having to use larger scale primary crushing units for initial break down. Significant trade offs may be scatter, and related extreme fines losses. It is hard to believe a primary blast would reduce sizes sufficient to allow direct heap leaching. Depending on porosity, you may need less than 1 inch size to heap leach effectively. To create even close that kind of breakage (colloquially called 'sugar blasting' ) you are faced with more drilling, (closer spacing) and more loading labour, smaller blasts, and perhaps the use of mats for ore blasts. It has been traditional to install large primary crushers which can be majorly expensive, to try to increase blast hole diameters, to increase burden (hole spacing) bench depths and increase blast scale in general in order to minimize removal costs per ton. Decreasing hole spacing, bench depth and increasing drilling and cycle time per ton would be the effect of going to increased percussive reduction. This part of the cost equation couples with a calculation of fines losses in ore blasting has to be factored against the decrease in comminution costs as the blast rock gets finer. It is tricky too to combine different bench heights for ore and waste. In open pit mining, it could be considered that if one could get to fist size rock, this is the equivalent of "sugar". I don't think holes burden could more than 6 feet on 3 inch holes to get this effect. Heavy mats would be needed. Powder factor would have to approach underground levels, close to 2-3 lbs per ton. It would take some experimentation. If you increase related blasting costs by 50%, (assuming these are half the total drilling and blasting cost), and increase powder factor by 50%, you might do away with crushing entirely to primary breakage size, and will get some decreases in costs of further comminution. The decision to increase powder depends on the costs of related production that attends the increased powder factor in comparison to crushing costs. With a small ordinary crushing cost in relation to drilling blasting and removal, it does not make as much sense to try to achieve efficiencies, as the dollar you are saving does not shrink faster than the accompanying cost increases in logistics. To put it in perspective, if you can do away with a 2 million dollar crushing plant, and a 400,000 dollar gen set, you save big capex dollars and loads of expensive electricity and wear maintenance. Especially in a smaller mine, that gets interesting, and might amply defray the extra drilling loading and removal time. In a softer limestone where breaking is easy, ore blasts fine you are only using a 100K crusher, reduction costs may only be a buck or two a ton, increasing powder by 25% and decreasing hole burden and bench depth by 50% has to be looked at more closely. If fines increase by some multiple, the fines losses could increase by an even larger factor, (very fine material can be 2 to three times the grade of mine run. If you went from 5% fines to 25% fines, and lost 25% of the fines to waste, you could lose 18.75% of your ore values, which might be prohibitive) so that effect has to be looked at carefully. EC:<-}

To: koan who wrote (94365)	10/6/2007 11:59:19 PM
From: hank2010	Read Replies (2) \| Respond to of 313046

Degerstrom knew how to drill and blast and move material! What is also significant in making money at .01 oz per ton (and they were one of the first at these low grades) was that they were smart enuf not to put much money into the operation. They drilled and blasted and put ore on the pad and then sprayed it for 7 months per year (freezing conditions for 5 months) for 5 years. It was not broken fine at all, but was porous enuf rock to allow the cyanide solution to eventually work its way into the fractures and dissolve the gold. Once it was on the pad, only major costs were to keep the pumps running.