Actually I have been thinking about this some and I think this could work out mechanically and the best narratively:
[] [Main] Build Iron Mine Bleeding Cliffs
[] [Secondary] Grand Sacrifice
[] [Secondary] Grand Sacrifice x2
Resource flow. +0 Econ and +1 Stability before Province actions. We also get Iron, when no one has anything better than brass. In general, it also radically increases the effectiveness of all our tools and we gain a major spike to productivity.
Provinces on Expansion will generate around 3 to 4 Econ. Possibly some Mysticism if they Main a Settlement. Any of the Econ generated here through Expand Econ will arrive before the mid turn
see this post.
Narratively I think we all agree that the Ymaryn equate "The Spirits are angry = disaster. And they need to be appeased."? So, looking at this vote we open the mine and we do a grand sacrifice, either before or after is fine. By doing the grand sacrifice we directly appease the spirits for our trespass into the earth, in the Ymaryn's minds to the best of their ability. I say this is the best of their ability because it is the option with the highest amount of generated Stability in one go besides Restore Order and RoO is more about corruption and crime than appeasing the spirits.
We also come out ahead in stability by doing this. I figure even if a disaster strikes next mid turn we will have in most of our people's eyes appeased them in regards to the mine so they will think the disaster cannot be related to it and thus Observance implies that something else caused it. Indirect weakening of the Weapons of the Gods, which may not be officially counted but it does set up a narrative for it to be questioned. Observance will probably not proc good or bad in the disaster, at least not in connection to the Mine.
Doing this with a Main Proclaim Glory could also work, as it maxes our Legitimacy, which will be useful if a disaster comes. It's a tradeoff of do we want 3(max) Legitimacy and 0 Stability or 2 Legitimacy and 1 Stability. Narratively it also appeases people by reassuring them that the king and chiefs know what they are doing. This does not have the spiritual appeasement element of the Grand Sacrifice vote, so I see it as being overall less effective in setting up a good narrative to prepare for a disaster, if one is coming.
We could do this to:
[] [Main] Expand Economy
[] [Secondary] Grand Sacrifice
[] [Secondary] Grand Sacrifice x2
This means we are at 2 Stability and 2 Legitimacy for the mid turn. I see Grand Sacrifice being our "Directly appease the spirits" option, which is why it is so effective and comforting. By appeasing them if the comet comes we cause some question to be made, but luckily it is one that can be directed since it is more honest confusion and fear that would be behind the uproar. Observance could be good or bad here, it varies if ignore means his prophecy gets forgotten or it gets out. Might even be a roll there.