This article was written by Snowden’s Mining Consulting Manager, Geoff Booth.
As part of a retrospective over a somewhat disparate reconciliation career, including time in the oil patch as a refinery economist and multiple front-line operational roles for base and precious metal miners, I’d thought a reflective commentary on some of the bigger reconciliation bugbears I’ve repeatedly encountered along the way worthy of a blog or three.
In brief, I thought it was about time to put some of these “material loss” incident reports which I’ve collected to use, rather than letting them waste away in aged PST folders, or on innumerable USB sticks. I’ve also felt that problematic resource-related reconciliation has been inadequately differentiated from poor operational and data handling practices. Interestingly, once I started to re-examine these various incidents, I was fascinated to see just how predominant these latter factors were when it came to metal loss.
Now, few of these bad actors will be new to experienced geological practitioners, however as this is just the first installment, if your particular reconciliation bugbear isn’t mentioned just yet, don’t worry, it’s undoubtedly coming.
Bugbear Numbers 1 - 5
1) Weightometers / Weighbridges: Tonnage Errors
When it comes to weightometers and weighbridges, I’ve found there tends to be two kinds of people on a mine site: those that always believe the numbers and those who never or rarely believe them, unless these instruments have been properly calibrated and maintained. Personal experience has forced me into the second category, together with some frank commentary and technical reports from a myriad of consultants who I’ve engaged over the years, the names of whom most, if not all readers of this post, would instantly recognise.
With this bugbear, one of the funnier(?) incidents I’ve witnessed is inspecting a brand-new belt scale which was busily measuring ever-increasing ore tonnages for a conveyor which had absolutely nothing on it. Like many of you no doubt, I’ve also had many interesting encounters with mobile fleets. These incidents invariably include watching tonnages change as trucks move from the bottom to the top pit and yet again when they finally reach the ROM. Better still is seeing an ultraclass haulpak exiting a shovel face fully loaded, with 43 tonnes displayed on its side panel. Now, I’m not sure time and space permits discussion of all my frontend loader incidents. Actually, as an ex-loader operator myself, I think we might let this one go through to the Keeper! Sufficed to say, these can often be the hardest numbers to reconcile, with loader operators sometimes hesitant to share their data with comments like: “Please don’t ask me today mate”.
As for weighbridges, I’m always fascinated when downstream operations or better still, toll-treaters use road scales that uniquely favour them over upstream partners. Whilst there may well be an underlying business reason for this (cough, cough), when you’re the one copping the hit, especially as often I have, it’s never much fun. Whether biased high or low, such scales need to be put on a permanent preventative maintenance program to minimise any “inherent subjectivity”.
Understanding that across a minesite, ore tonnes disappearing, only to reappear later, is a common problem, especially when trucks and conveyors of different vintages and technologies are in play. Over time, most mine geologists become adept at knowing which weightometer / bridge numbers to trust and which to ignore. A little bit of forensic (CSI) accounting often allows them some degree of comfort when stating: the metal’s coming back, but we’ll have to let the numbers sort themselves just a little bit longer and while we’re all here, can someone please get those damned weightometers rechecked?
2) Blasting: Overcharging / Undercharging
While blast designs have come a long way, particularly from a modelling perspective over the last decade, geologists and engineers alike are also paying a lot more attention to blast movement monitoring, especially in open cuts. So, as I look at some of the ore loss or extreme dilution incidents, virtually all are linked to excessive movement and unplanned over-break. Ore thrown on waste or more commonly, waste unintentionally admixed with ore has certainly been a bugbear of mine, with no shortage of round table meetings with Drill and Blast engineers.
Now, to be candid over the years, I’ve dodged the odd piece of fly rock outside an exclusion zone or returned to my pit office to see a broken window and rock shards lodged in a wall. While no one, including geologists, wants to see excessive oversize or a chronically blocked jaw crusher, the current emphasis on minimal, selective, or planned movement (e.g. power troughs) needs to be encouraged and the emphasis on blasting selectively maintained.
While in the past, we may have jokingly referred to a “LEO” (Lower Earth Orbit) blast, I’m confident that such incidents are dwindling over time, as quality control measures lessen the patchy free faces and drilling patterns which combine with poor stemming and loading practices, to cause them. For operations that might not be able to afford say a BMT style (ball monitoring) solution, comparatively simple process controls and even risk assessments, often go a long way to reduce dilution and prevent ore loss.
In terms of underground incidents, whilst occasionally I’ve returned underground to see vent bags shredded across an entire level, more often than not, it’s been frozen rings or partial hang-ups that have loss the operation ore, and metal on the day. Hence, when explosive energies are modelled poorly for a given rock type and its assorted geotechnical parameters, having to continually slash because of undercharging, has its material consequences as well.
3) Survey Inaccuracies: Stockpile volumes (COSP’s, ROM’s etc), bad set-outs, pick-ups
Radar sensors or not, I don’t know how many crushed ore stockpiles I’ve monitored that have “magically” increased in tonnes as they’re drawn down with notional “dead zones” that turned out to be very much alive, well after the fact. Certainly, a great part of annual shaft shutdowns at underground operations, is witnessing an underperforming resource suddenly overperform and in the matter of week, recoup “lost metal” from a reclaimed COSP!
The same is true with rehandled stockpiles that miraculously last a week longer than they should have or temporary ones that were missed entirely over a series of EOM surveys. I especially love those “secret stockpiles” that turn up in the confines of a mill, of which only a select few are aware, which return quasi- concentrate (e.g. 15%) grades. I’ve seen such stashes instantly rebalance what was a significant metal deficit, much to the relief of the mine geologist (me).
In the same vein, beware of those continually growing ROM’s! Once they’re 5 years old, it’s always good to take them back to their benchmark / design RL, the last metre of which we all know was built using low grade ore at the insistence of the Senior Mine Geologist!
Accordingly, when it comes to stockpile survey volumes, remember to use a suitable broken density to as part of an ongoing validation process. If you treat these numbers with the healthy skepticism they deserve and learn from any mistakes made whilst building them, your expected and actual metal contents should progressively align over time.
Now for underground operations, I have incident reports from survey inaccuracies which have resulted in a “misplaced orebodies” and production hole mark-ups which regrettably, badly missed their marks with a few Golden Gaters (i.e. bridges) to prove it. In addition, I’ve seen how quickly missing a pick-up can put you outside an orebody, and even a trifle too close to existing infrastructure.
Meanwhile, in open cuts, I’ve found ore block mark-outs surveyed in poor weather or in early morning or late afternoon have a greater “propensity for oversight”. On one occasion, a poorly maintained GPS / Total Station forced me into the pit at 2:00AM, trying to figure out why a no-dig line and ore mark-out didn’t match. Good shovel operators who pay attention, especially on night shift, are hard to come by!
Needless to say, current survey hardware and software is both remarkable and usually very accurate. However, for someone like me who was trained using optical theodolites (i.e. transits) and hard-copy maps, I’m very cognisant of how easily complex instrumentation can fail us, especially if we’re not watching. Now, is it just me or did paper set-outs get checked with a lot more care all those years ago?
4) Procedural Failures: Geologist / Spotter / Geotechnician Mis-Communication
When it comes to ore management and/or dilution prevention, mine geologists tend to be pretty fanatical. After all, it’s their job and if they’re anything like, me, it becomes very personal, very quickly. This incident series relates to some of the most avoidable ore loss incidents I’ve observed, linked either to miscommunication or simply no communication at all.
Accordingly, this is where grade control staff are not contacted on time or at all when ore movement needs monitoring or direct intervention. My incident files bear witness to numerous repeat offenders, among pit superintendents or underground shift bosses alike, “forgetting” to alert staff when ore and waste have to be visually segregated, or even to police where ore carting has ceased.
Ensuring that deleterious material types are stockpiled separately is another “incident favourite” of mine, with numerous instances of clay-rich and high arsenic ore mistakenly making its way onto a ROM. I don’t like thinking about all of the time and money spent rehandling such material either, but it bears remembering that we have the technology to stop this, be it radios, phones, emails or just speaking to staff at daily communal meetings.
Hence, in open pits where communication works well, I have seen head grades rebound instantly when night shift ore movements were prevented, or the available spotter was acknowledged, and their decisions respected. In underground operations, where procedures are followed, and communication undertaken, I’ve seen serious overdraw eliminated in sub-level caves and with it, cessation of chronic waste ingress / piping.
5) EOM Spreadsheets: Geologist / Engineer / Metallurgist – Heal Thyself
As much as I have been a user and abuser of EOM spreadsheets over the years, even before dedicated reconciliation software solutions were available for mines and refineries, I knew the latter was the best long-term answer to the patchy metal reconciliation reporting practiced by our industry. Whilst our colleagues in the energy sector have gone a long way to standardising metrics and automating their reporting systems, regrettably the mining sector has been less successful in this regard. Even where such systems are implemented, its often done half-heartedly by an upper management who look at costs before benefits.
A fascinating incident I like to recall attempted redress a sizable imbalance at a mine site which appeared to bleed metal. When I arrived and examined the 6 linked EOM spreadsheets, it became clear that each was so seriously flawed that there was little chance of successfully retrieving individual monthly reconciliation data with any degree of clarity. Post-automation, I was pleased to see how quickly transparency returned, with the immediate discovery of a serious and previously unidentified density issue.
Hence, unless your operation is exceptionally simple, when it comes to spreadsheets, I would resist the temptation to EXCEL yourself a solution and seek a proper database to avoid those intractable errors that invariably crop up as a result. I am of course reminded of some of the more celebrated (infamous?) instances of spreadsheets gone wrong for a myriad of banks (JP Morgan etc), who have relied on the numbers that they generated, without understanding the potential for errors that may lay hidden deep inside.
So, let’s continue the conversation online and ideally among our fellow professionals to redress some of the issues which I’ve cobbled together here. I’ve got at least another couple more reconciliation installments to come in the weeks ahead, which I hope everyone will enjoy reading as well.