So I went ahead and put together a makeshift data table of the costs and profits of mining for low level players (mainly only have level 1 mining). It's pretty rough, and could have a look over or 2 for errors or miscalculations. But I think it gives a decent overview of the profession. Well, lets have a gander.
Spark (sparkly) - market sell = 6c.
Blue (Beryl) - market sell = 4c.
White (Dullite) - market sell = 3c.
Node energy cost 12; time 20s.
Basic food; 23c = 23e ( I only suggest this due to it's easier not to over eat, thus wasting money per energy gained)
Median ore obtained: 7
Math time :D
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Spark spawns roughly every 5-8 minutes (for the sake of the equation). Near 8 "mines" per node, which would be 2m40s, and 96 energy used. Food needed to restore would be 4 (23 energy per food at 4 times, is 92) costing only 92c.
☻Food cost: 92c
☻Time taken to find / mine node: 9m (again, sake of later equations)
☻Total ores gathered: (how many times you mined the node * 7); 56
☻Profit from ores: (How many ore you obtained * vendor price of ore)
=> (56*6) => 336c
☻Net gain: (profit from ores - cost of food) => (336c - 92c) => 224c
☻Gain per "run": net gain / time spent => 224c/9m => 24.8c/m
☻Gain per "hourly run": "run" gain * 60 => 24.8c/m * 60 => 1493c/h
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Blue spawns are pretty common, not quite as common as white, and tend to be seen at least every 1-2 minutes. Again, same median ore looted, and same times / energy.
☻Food cost: 92c
☻Time taken to find / mine node: 4m (sake of conversions)
☻Ore gathered: 56
☻Profit of ore: 56*4 => 224c
☻Net gain: 224c - 92c => 132c
☻Gain per "run": 132c/4m => 33c/m
☻Gain per "hourly run": 33c/m * 60 => 1980c/h
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White spawns are the top dog of common, you should be finding one at most every minute. Loot amount, time, etc, all the same again.
☻Food cost: 92c
☻Time taken: 3m (kind of short, but I hate conversions :D)
☻ore gathered: 56
☻Profit: 56*3 => 168c
☻Net gain: 168c - 92c => 76c
☻"run" gain: 76c/3m => 25.3c/m
☻"hourly run" gain: 25.3/m * 60 => 1520c/m
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Now this is just a sample table, not including many, many other variables (like levels of mining, if other people help you, if you find gems, AH supply and demand vs vendor, spawn rates of nodes, time running back to vendor, etc). Just a rough, rough idea of how much cash flow is going into mining for a new player. As it seems for now, blue ore is the most profitable to harvest and sell directly to vendors. I know spark ore vendors for more, but it's rate of loot vs vendor price just isn't comparable to blue's ore rates & vendor prices.
From this data (how inclusive it might be) the priority chart for mining would be blue, sparkly, white. Don't bother with iron for now, as it's vendor price is very low, and doesn't spawn with the other ores deep in caves. If you can, buddy up. It helps remove non sparkly nodes faster, and adds a bonus to looting ores. Also, it's nice to not be alone for so long. With a buddy, time to mine a node also drops, which reduces energy costs, which improves net profit gains. Always a plus.
PS: don't forget to dump some ore into the giants, as the food vendors in caves don't sell drinks, and your mod will drop over time, thus lowering xp gains. :)