I'm sailing as First Mate on a 730 foot Great Lakes ore carrier (self-unloader) that loads iron ore in Escanaba Mi. on a regular basis. In Escanaba the dock is owned by Canadian National Railroad. Cargo is brought into town in trains and stockpiled. Ships are loaded by an ancient belt system, with a movable loader on tracks, either off the stockpile or directly out of train cars. A typical load is a combination of both. We usually take approx 32,000 Gross tons of taconite(iron ore) per load and it takes 12 hours when things are running good with the dock systems. Up to 24 hours PLUS, when things are NOT running good on the dock. There is only one loading dock operating, although there is room on the other side of the pier for a ship our size to moor and wait. As far as bulk loading docks go, its an easy dock for crew to load at, just never know how long it might take.
There is a stone/coal dock in Escanaba where cargo is delivered for transhipment up to the mines. No ship loading is done at this dock. We usually haul stone into Escanaba, offload at the stone dock, then shift over to the ore dock for our southbound cargo.
Marquette also has an ore dock, I think its an older gravity chute dock. I'm not sure the specifics of that port as I've only been in there a few times. Small harbor tho.
Green Bay is more of an destination/unloading port than a loading port. Cargos going in there are usually more like stone and coal as well as some pig iron and cement. Several docks are used for unloading and most vessels are self-unloaders.
Hope this helps...