I don't think that it is safe to say at all. It seems wildly speculative to me. It is also not as relevant from a cost standpoint as how many miners per ton are involved for each of the task-teams assigned.
My first employment was in 1966, after finishing college and my 4 year military obligation. I spent two years in training to become a professional cost estimator for construction. So, I understand the thousands of factors that have an effect on costs. I've spent a few hours here and there over the past six months reading and learning how they estimate costs for drift mining a placer gold mine. There are books published that are several hundred pages that cover only particular types of cases and each points out how radically different it is from one mine to the other. The whole issue is many parts:
What is required? (partial list below)
.. what crew tasks are involved?
.. number per crew
.. working hours versus paid hours
.. the unit costs per task for what a crew can do
.. what logistical limitations exist
.... feasible tons/ft/sec transit time and return time
.... equipment access and movement time
Try to answer these two questions accurately to see how good you are as an estimator.
1). If one man can roller-paint, prime and finish, and cleanup afterwards the walls and ceiling of a 20 foot long, 2 foot wide by 3 foot high tunnel, in 4.25 hours, then how long will it take 12 men to do that job?
2). If that tunnel were instead a vertical shaft that reached upwards from a ceiling, and the ceiling was 32 feet up from an irregular sloping floor, and there was no other access, and the paint fumes were toxic, and the one man had to do all of the work and paint all 4 sides of the shaft; how long would it take?
The point here is that without a thorough knowledge of the physical layout and the access points and the nature of the channels and shafts and how many miners are assigned to what tasks... etc., nobody can really say with any accuracy what is good or bad productivity. This is why they do time studies. Once you have a few time studies of a few of the different "typical conditions" there then you can do a somewhat accurate productivity projection.
I've read that sometimes those channels are loose enough rock that blasting required is minimal.... once loosened then a miner working a bar brings down many, many tons. Other cases the cemented-nature of the ore requires extensive blasting.
I've read that in the 1920's one miner could haul about 1 ton of ore out of a half mile deep drift mine per day. Yet, in another case with highly mechanized drift mining they could remove over 2,000 tons per miner per day.
How many tons of rock per day are they removing while advancing towards the black channel?
Estimates require meaningful dimensions on as many of the factors involved as possible or they become merely guesstimates or worse, wild speculation.
At this point I believe we are all at that wild speculation stage of estimating.
