Baltic:
You are correct in your observations about the early stages of city building and the construction of sanctuaries.
It's very obvious that in the early stages of building a city like Athens or Sparta which will require say four sanctuaries we will not have all the materials available at the 1st sanctuary site. But we can start planning for the location of materials for the 2nd, 3rd, and 4th sanctuaries.
If you plan and think out your cities in advance and know where you will be building your future sanctuaries you can prepare the sites before hand and have the majority of materials available at the site before construction takes place.
In the case of the very first sanctuary you are absolutely correct. Your approach of using "Accepting" SYs at the mining site and "Getting" SYs at the sanctuary site would be the most efficient. This is true because as I indicated there seems to be an unlimited number of carts available at the "Getting" SY to deliver the material for the artisan. And the key is while the materials are being delivered to the artisans the SY's two "Getting" ox carts will be bringing in material from the mining sites.
I would also strongly recommend using detached SYs or trading posts as I indicated in the write-up. This is because if you connect the mining site to the sanctuary by roads your artisan may request materials at the SY located at the mining site. If it does, it may be comming in at the extremely slow rate of 1 slab of marble/cart (assuming 1st Phase). It is more efficient to detach the sanctuary site from the mining site and have the marble delivered at 4 slabs/cart to the sanctuary site when it can then be accessed at the slow rate of 1 slab/cart.
The glyph I drew would be more realistic for say the second, third, or fourth sanctuary site where your city is now over producing or importing building materials and you have the luxury of storing your excessive building materials at the future sanctuary site.
Good gaming,
Vriesea