The motivation for mine exploration can lie anywhere between recreation and research. At one extreme is the fun and challenge of opening new routes and at the other is the slog work of making surveys and collecting data that help us to understand more of the way mines were worked and of the reasons contributing to their success or failure. An understanding of the geology is one essential component of this understanding.
At this latter extreme a simple question arises, why should geologically ‘amateur’ mine explorers collect geological data at all when the country is already covered by detailed geological maps made by professionals, ie academic and institutional geologists. Two reasons stand out: first, geology on maps is essentially only a 2D representation; perhaps 2-and-a-bit D in very rugged terrain; second, professionals, like the rest of us, are not imune from error. A true 3D picture of the subsurface is seldom fully attained by anybody but clearly the average inclination of a lode measured throughout a vertical depth of, say, 200 m in mine workings is more representative (and useful) than an estimate based on a surface outcrop of 2 m height (if one is lucky), particularly in glaciated country where bedrock may be disturbed. I know of many cases where the surface-based geology on ‘official’ maps is at variance with Victorian mine plans and there is no doubt that the latter are correct. There is also a question of scale; ‘official’ published maps are commonly at 1:50,000 scale whereas mine plans, ie what the mine historian needs, are commonly at 1:500 scale. One can add other reasons; some professionals are these days not always allowed to venture underground on HSE grounds; and again, subsurface accessibility is under constant threat and ‘amateur’ data today may be better than waiting for ‘professional’ data sometime in an uncertain future.
What I wish to argue below is that with very little ‘training’ the average mine explorer can collect geological data of real value for research purposes. The reasons for this opinion are:-
a) many explorers have developed a good sense of observation, if only for safety reasons. They watch for signs that roof rock may be unstable or that they may be walking on a false floor. Noticing that the appearance of rock is changing is the first step in asking ‘how / why ?’ and in deciding what may be worth measuring.
b) there are probably many more explorers than underground geologists. I have been fortunate to see mine workings that most geologists could not thanks to companionship (and SRT instruction) from experienced explorers but ultimately there will be places where young explorers can reach but which old geologists cannot. In these cases any data, provided it is sound, is better than none.
c) many explorers are already familiar with, or make, simple compass / tape surveys so scope for ‘added value’ by recording geological data is already there. If you have a compass suitable for such survey the only additional piece of equipment needed is a device for measuring inclinations (a clinometer).
d) much data of real value geologically is actually rather simple to record.
Rock strata, and mineral lodes, are not homogeneous; they contain internal fabrics relating either to compositional differences during their formation (eg sedimentary bedding) or to fracturing during later deformation (eg joints, faults). Surprisingly many of these fabrics are essentially planar like tiles of variable thickness and their orientation is thus simple to measure by recording their strike and dip. Strike is the orientation of the trace of a dipping surface (eg a lode or sedimentary bedding) where it intersects the horizontal, the maximum value of the dip is hence perpendicular to the strike. Strike and outcrop trace on a map thus coincide only if topography is flat or dip is vertical.
Assuming that some explorers fancy trying their hand at some basic geology, what advice can I give as to what / how to record observations of rock fabric. If possible try to do a trip with an experienced geologist and watch / ask questions. Most mine explorers know the difference between a cross-cut and a drift but try to pin down exactly what the observational basis for such belief might be – lack of mineralisation alone is not decisive, many lodes locally pinch out into barren ‘joints’. There is seldom need to record everything; learn to sample selectively focussing on regions where the rock type / fabric is clearly changing rapidly. Changes in rock type may be capable of being correlated with similar changes seen at surface, helping to build a 3D picture. Changes in lode fabric, eg ‘jogs’ in azimuth, may similarly be correlatable between levels and are often prime controls on the attitude of ore ‘shoots’.At first keep it simple. Focus on the distinction between country rock and lode. Where features of either look unusually interesting or their interpretation would benefit from discussion with other explorers it is time to consider making some form of record. If so, I would recommend:
- photographs, better than nothing.
- photographs with a scale / orientation and in both close-up and more contextual view, better still.
- photographs as before but accompanied by notes (written at the time, not from memory), rather good.
- photographs as before but the notes additionally including a precise location (on a plan or in terms of distance / bearing from a known feature and spatial orientation data for the rock fabric photographed (and reference to any samples taken), top marks !
Your records, as with any data, are ultimately useless if kept private. I believe most if not all of the geological data that we can collect as mine explorers should be in the public domain without copyright restriction as an aid to future research. I have no expertise in data storage / dissemination but it seems to me that web-based facilities such as those pioneered by aditnow for mine photography may contribute towards this goal and I have written the above article in the hope of starting debate on these issues. Two obvious areas of interest might be:
- sharing of surveys containing geological data
- a forum for discussion of problems encountered in the identification of geological features, an idea put to me by Roy Fellows
David James