Ah yes. I did something quite similar. Not for all resources, but for a single resource. First i added a resource producing skill for each resource. For example:
"vulcanology" : {
"name" : "Vulcanology",
"gainChance" : {
"might" : 7,
"magic" : 1
},
"basic" : {
"images" : {
"small" : "skills/SulfurSmall1.png",
"medium" : "skills/SulfurMedium1.png",
"large" : "skills/SulfurLarge1.png"
},
"description" : "{Basic Vulcanologist}\n\ngenerates 1 sulfur per day.",
"effects" : {
"main" : {
"type" : "GENERATE_RESOURCE",
"subtype" : "resource.sulfur",
"val" : 1
},
"xtra" : {
"type" : "GENERATE_RESOURCE",
"subtype" : "resource.sulfur",
"val" : 50,
"valueType" : "PERCENT_TO_BASE",
},
}
},
"advanced" : {
"images" : {
"small" : "skills/SulfurSmall2.png",
"medium" : "skills/SulfurMedium2.png",
"large" : "skills/SulfurLarge2.png"
},
"description" : "{Advanced Vulcanologist}\n\ngenerates 2 sulfur per day.",
"effects" : {
"main" : {
"type" : "GENERATE_RESOURCE",
"subtype" : "resource.sulfur",
"val" : 2
},
"xtra" : {
"type" : "GENERATE_RESOURCE",
"subtype" : "resource.sulfur",
"val" : 100,
"valueType" : "PERCENT_TO_BASE",
},
}
},
"expert" : {
"images" : {
"small" : "skills/SulfurSmall3.png",
"medium" : "skills/SulfurMedium3.png",
"large" : "skills/SulfurLarge3.png"
},
"description" : "{Expert Vulcanologist}\n\ngenerates 3 sulfur per day.",
"effects" : {
"main" : {
"type" : "GENERATE_RESOURCE",
"subtype" : "resource.sulfur",
"val" : 3
},
"xtra" : {
"type" : "GENERATE_RESOURCE",
"subtype" : "resource.sulfur",
"val" : 150,
"valueType" : "PERCENT_TO_BASE",
},
}
}
},
Then i modified the resource producing artifacts. For example this one:
"core:eversmokingRingOfSulfur":
{
"bonuses" : [
{
"type" : "GENERATE_RESOURCE",
"subtype" : "resource.sulfur",
"val" : 50,
"valueType" : "PERCENT_TO_BASE",
}
]
},
I hope i do not need to repeat the standard bonus here. The idea is:
A normal hero does not produce any sulfur. The ring produces 1 sulfur. The extra bonus adds 50%, which results in zero.
A resource specialist produces 1 sulfur. Add the ring, that produces another sulfur. Add 50%, which produces a third sulfur.
The skills produce a little more. So to get the maximum out of such a hero, take a sulfur producing specialist, add the vulcanology skill, and add the sulfur ring. All to the same hero. That should result in a maximized production.
Btw. i’m still searching for good names for these skills. Currently i have:
- ore: prospector
- wood: woodcutter
- crystal: mining
- gems: geology
- mercury: alchemy
- sulfur: vulcanology
I think, prospector and alchemy are already quite good. The others might still need a better name 
