The recipes
A furnace (20 stone + 2 copper ore) smelts: 5 copper ore → copper bar, 5 iron ore → iron bar, 5 gold ore → gold bar, 1 quartz → 1 refined quartz, 1 iridium ore → iridium bar (needs the gold-tier furnace upgrade path... practically: furnaces are cheap, build banks of them). Bars feed every upgrade path: tools, sprinklers, lightning rods, kegs and preserves jars.
The refined quartz loop
Quartz is abundant in the mines and smelts into refined quartz — the ingredient for quality sprinklers, lightning rods, crystal paths and more. A mine run that looks like "just quartz" is actually a sprinkler-material stockpile. Keep a furnace bank beside your chests and process on rainy days.
Bars as a barometer
Your bar stock tells you when to upgrade what: copper for the first tool tier, iron for quality sprinklers and the steel pickaxe, gold for quality sprinklers and slime incubators, iridium for the endgame (iridium sprinklers, barn/coop top upgrades). The furnace bank turns mine runs into permanent farm infrastructure.
