• Scott Close

Macro, Meso, Micro: a Note on Scale


Putting together maps and figures for the upcoming 'financing season', as well as various geology conferences in the new year, and I've run into straight into an issue that always seems to be an elephant in the room.

Scale

Not fixed, but the relativity of.

It is said geologists are of two types: lumpers or dividers.  


Those who lump, tend to be good regional-scale mappers, always considering 'the forest'.  


Those who divide, tend to be good deposit-scale mappers, always considering 'the trees'.


However, problems arise when trying to indicate on the same map both data styles collected.... How important is this particular fault?  ...What is the relevance of this one type of texture?  ...Why didn't geologist A pick up on the all of these different lithologies mapped in the same area as geologist B?  Who is right?  When?

Principally, one must ask oneself what is the question to be solved, and scale the relevance and data collection appropriately.

Microscopic    Used: Not Often Enough Level of Effort: High     Scale: Thin Sections Frequently the overlooked within the mining industry, microscopic clues tend to carry MASSIVE importance relating to solvency of both meso- and macro-scopic concepts.  Outcrop identification, drill core interpretation, and the solid data provided for both- by microscopic investigation- can quickly dispel myth and incorrect interpretations.  Consider the microscopic to be the ace-in-the-hole, its' shear irrefutability and minuscule nature make it one of the strongest datum of forensic evidence, and easiest, that can obtained.

Mesoscopic     Used: Often Level of Effort: Moderate     Scale: Outcrop Any given fracture, vein, or texture change in a volcanic rock carry, by themselves, very little weight when investigating the big picture.  These data as a whole, however, can yield integral solutions to some of the most prevalent questions.  Unfortunately, the tenacity to compile massive amounts of seemingly-not important data- which can result in ambiguous interpretation until some critical threshold is reached- is not often had by most geologists.  Only the best field mappers understand the 'continuum concept', wherein cracking small codes, one slow step at a time, results in winning the case.

Macroscopic      Used: Often, for the wrong reasons Level of Effort: Easy Scale: Mountain Ridge The freedom of the hills.  To be dropped off in a helicopter, and point oneself toward a distant glacial valley or ridge, and find your stride.  Regional-scale mapping carries with it the ambiance of distance.  Just about every field geologist loves the opportunity to prospect, flirt with interesting rock when desired, and brush off time-wasting finer details that have only mesoscopic culpability.  


Unfortunately, however, too often companys state "Competitor A staked hundreds of claims in an area along the same [belt / trend / district] as we did, only 100 kilometers away, so therefore our exploration potential is GREAT!". Wrong.


We've all heard that saying about 'chasing elephants in elephant country'; but the truth about elephant country is that it is expansive and enormous, and it's better to focus in on hotspots.

Why is any of this important

Most new geologists to either academia or the industry are presented with an opportunity to collect field data, at any or all three scales.  The quality of the data, however, is usually filled with holes and traps ripe for mis-interpretation because of lacking relations among the three scales of observation.  Insufficient data at any of the micro, meso, or macro scale results in potentially fallible hypothesis that can have disastrous results.

Do yourself a favour.  During the scientific process, consider the implications of a datum at all three scales.  

  • When working the macroscopic, consider why and which data are important- many economic porphyry intrusions, for instance, you'd be lucky to trace for even 200-400 meters- so to avoid skipping over the next economic discovery, consider the type of data that needs to be observed, the type of data that has relevance to ore deposit controls, such as: basement structure, lithologic / sedimentary facies changes, age dates.

  • When working the mesoscopic, practice collecting- describing- as much texture data as possible- what appear to be augite grains in an altered rock might actually be accretionary lapilli- the genetic difference between coherent vs clastic rocks can have incredible implications on ore deposit formation due to permeability and vectoring.

  • When working the microscopic... all is revealed. If you've done good work at macro and mesoscopic scales you'll find many of the features present at other scales are carried through to the smallest grains.

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