You are incorrect that olivine mining at a large scale would incur tremendous energy costs, it will not. I would suggest you check out this model of a 5,000 tonne per day open pit mining for porphyritic rock. (This model also includes 5,000 tonnes per day of "waste" rock which will likely not be wasted in our use case) http://costs.infomine.com/costdatacenter/miningcostmodel.asp...
In this model, which is not in any way optimized for environmental efficiency, it requires a diesel fuel quantity of around 4,751 liters/day to mine the 5,000 tonnes. At 2.68 kg of CO2 per 1 liter of diesel, that generates 12,732.68 kg of CO2 per day. That 12,732.68 kg = 12.73268 tonnes of CO2. The 5,000 tonnes of olivine mined will eventually weather and sequester 6,250 tonnes of CO2 (1 tonne of olivine sequesters 1.25 tonnes of CO2), for a net capture of 6,237 tons at the mine.
We have life cycle assessment that calculates the CO2 penalty and loss on efficiency, including milling and transport to locations less than 300 km (186 mi) at around a 4% loss .
Just for your information and for others, from a financial perspective the mining in that model costs $7.32 per ton, and then the transport and milling/crushing only costs about $3 per ton, so olivine could be transported to a beach at around $10/ton, with the price per ton of CO2 sequestered at less than $10.
You are also incorrect regarding the mining impact. The mining of things like shale requires fracking and the injection of sand and chemicals, our mining is simply open pit. Essentially, you open a pit on the surface and simply dig it up. As mentioned above, it is not all that energy intensive either.
For global CO2 level removal in terms of mining, it would likely require 30-50 mines in the wet tropics, preferably at a level of greater than 100 million tons/year (due to economies of scale). There are large reserves on every continent and plenty near coastlines. If you wanted to open fewer mines, you could theoretically find a few large reserves. For example, there is an open pit mine in Bingham Canyon that has an excavated volume of over 25 km^3, which would be the equivalent of 2-3 years worth of the volume of material needed.
Don't worry about this idea getting "tossed out with the bathwater," if anything we will actually be removing CO2 from the bathwater and de-acidifying it at the same time ;)
 Environmental Life Cycle Assement of CO2 Sequestration Through Enhanced Weathering of Olivine https://projectvesta.org/science/#dflip-df_978/1/
I would push back, however, on the land impacts of mining. Open-pit mining is exactly what I was referring to, and it doesn't have a good reputation with me. I have encountered many open-pit mining projects which were extremely destructive with regards to habitat, watersheds, groundwater, etc. (Arguably much moreso than things like fracking, TBH.) A massive increase in open-pit mining therefore sets off significant alarm bells for me.
Now, it's possible that I'm suffering from selection bias here: I only hear about open-pit mines when they're bad, and when they're benign they sail right under my radar. Maybe, on average, they're fine.
But that's not the kind of thing I'd take on faith. What would convince me is a site-specific Environmental Impact Report which illustrates how a 100MT/year olivine mine could operate without causing severe regional damage.
This project proposes mining at a scale that is cumulatively about 8,000 times greater than Glensanda. But if they could all be done so sensitively, then indeed, perhaps it could work.
I've still got a lot of cognitive intertia about the impact of open-pit mining, and would definitely need more convincing about this. But I'd be open to being convinced.
So probably a better metric is total length of coastline. The UK has 12,429km of coastline, out of a world total of 356,000. So that would imply 279 Glensanda-sized quaries in the UK.
Good news for the UK (and bad news for everyone else): weighting by amount of harm done to the climate wouldn't work. In addition to being located near coastlines, the quarries need to be located in tropical and subtropical regions. So in fact there wouldn't be any quarries in the UK.
Looking at this source: http://chartsbin.com/view/ofv, it appears that there's about 275,000km of suitable coastline. The top 3 countries would be: Indonesia (1,592 Glessandas), Phillipines (1,056 Glessandas), and Australia (749 Glessandas). I'm not sure whether or not that's feasible. But at a smaller scale, as a partial solution to sequestration, it seems within reach.
How does this compare to the lifecycle net efficiency of other methods of carbon capture/abatement, e.g. wind turbines, nuclear solar panels/farms, EVs, afforestation? Any references for such estimates?