Golden Hematite is a type of ore found in Wild Hearts and it's used primarily to craft or upgrade certain weapons (opens in new tab). Many of the materials you'll farm come from the enemies you'll be facing but some, like Golden Hematite, don't require bloodshed to obtain. You will need to progress through the main story to access it, however.
Just getting started in Azuma? No problem. These Wild Hearts tips (opens in new tab) should get you started on the right path. Or if you want to know how to easily find all 50 tsukumo (opens in new tab), there's a guide for that too. That said if you're keen to start upgrading your weapon, or craft a new one, here's where to find Golden Hematite in Wild Hearts
Wild Hearts Golden Hematite location
Golden Hematite is found in Akikura Canyon, but only after you've reached Chapter Three in the main story. Once you progress to this point, you can find clusters of the ore embedded into the canyon walls: it's easy to spot as it's bright yellow. If you collected Mirror Stone earlier in the game, you'll find that Golden Hematite replaces that resource from this point onward.
If you're looking for a good farming spot, the cave system to the north of Akikure Canyon is a good spot, though the nodes can appear anywhere within the canyon area. There's also a good amount to the east.
Be aware that these nodes don't have a 100% chance of yielding Golden Hematite, so don't be disheartened if you don't get the ore right away.