Given the givens, "something weird" is unfortunately a lot more likely than "someone did something". She stares at it, pokes it, and stares at it some more before remembering the tree-cube and realizing that maybe this is what veins of metal look like when you're mining in this reality. Does hitting the metal square with the copper pickaxe produce an effect?

It pops out of the wall with minimal effort, collating into a neat little lump of lead ore.

Neat! And she can probably pick it up and put it in her bag much more easily than she could with the kind of block of lead she's used to, yeah? She'll do that and then keep digging at the back of the cave, at least if her pickaxe handles stone as well as it does lead.

Yeah, it's heavier than wood but it's still manageable.

Stone's actually a little bit easier. Also, stone collates itself into perfect cubes, like the wood did. Dirt does too, when it comes up, and takes only one halfhearted blow of the pickaxe to dislodge.

(Stone and wood can be used to craft arrows!)

It's not long before she breaks through into another cavern. This one is dark, no natural light coming in except from her tunnel.

Margaret's eyes, with their reflective layers and slit pupils, are optimized for night vision, but she can't see more than outlines--and something in this new cavern is dangerous. She pulls out one of her torches and intends it to light before stepping through. 

It lights up! The flame doesn’t seem to emit any heat, just light.

The torchlight reflects off a glittering red crystal in the shape of a stylized heart. There’s a living skeleton standing next to it, which turns to her and growls.

And that would be the dangerous thing. It's an environmental hazard rather than a person, so she sees no reason to let it go on being dangerous. She drops the pickaxe, pulls out the copper-and-amethyst staff, and lets the skeleton have it.

The skeleton has it! It takes five shots to put it down.  The skeleton continually tries to shamble towards her, but is knocked back by the staff every time it tries; the overall effect is kind of comical. 

Eventually it explodes in a shower of bone dust. It drops a silver coin and a mining helmet. 

The fact that it clearly wasn't wearing the mining helmet it dropped isn't really surprising at this point, but it's still funny. She wonders if she can even wear it with her horns on, and tries finding out by putting it in the general area of her head.

It fits somehow! The lamp on the front turns on, illuminating the cavern slightly more effectively than her torch. 

Also, she’s now wearing a transcendently ugly miner’s helmet. This thing is the exact opposite of fabulous.

Yeah, no, she was never going to keep wearing it. Blech. It can go in her apparently bottomless bag with the silver coin and the blasting staff; maybe she can use it for scrap metal at some point. Now, how about that glowing heart thing? That looks important in a good way.

It emanates a soft warmth and the smell of cinnamon! It’s stuck to the ground, though. She might need to dislodge it somehow. 

Mmm, nice. She definitely wants this thing. "Whack it with the pickaxe" seems to be a good bet for most things around here, but this one looks fragile. She'll whack the ground underneath it with the pickaxe instead.

There’s a crystalline tinkling noise, the heart shatters, and a significantly smaller crystal heart leaps into her hand. It is apparently edible.

Edible, really? Well, she doesn't sense any danger when she holds it to her lips, so, uh, okay. Om . . . nom?

It's like a cinnamon hard candy that, against all odds, isn't terrible.

In fact, it's great. The taste of cinnamon is accompanied by a spreading warmth and something almost like the sensation of being hugged. Then the feelings fade, leaving her with just a faint warmth at her core.

Ooh, how nice! Score one for eating shiny rocks she finds on the ground, apparently. She keeps on mining further, if there's nothing else in this chamber.

In her mining she discovers: some more lead ore, two more heart crystals, a good amount of copper ore, a generous purse's worth of copper and silver coins, an unidentified greenish metal ore, and...

okay, this one's pretty weird. She discovers a few cubic feet of red-and-black ore. When she tries to mine it, it doesn't budge. In fact, even if she mines out all the dirt around it, it just... stays there, floating stationary in the air, throbbing with red light.

She eats one of the heart crystals and bags the other to take back to Eric and see if he knows anything else that should be done with them. She also wants to ask him if the coins are just purer forms of metal, or if there's an actual bank and economy out there somewhere, possibly run by more robots. 

The floating glowing ore is seriously cool, but she might just have to leave it. Maybe it needs a different tool to extract it. Regardless, now seems like a good place to turn around and start heading back to base, where she can have another meal and figure out what to do with her haul.

Night has fallen. When she exits the cave, a zombie shows up (presaged by a dangersense ping) and groans as it approaches her.

It's slow enough that she goes with the copper sword, this time; if it tries to dodge it finds itself dodging right into her blade. 

It doesn't try to dodge.

The copper sword remains really shitty, but it's good enough to kill a zombie. The zombie explodes messily, leaving behind a copper coin and a broken iron shackle.

The groans of more zombies echo through the hills.

She scoots up the decidedly meh loot and heads for her house, killing any zombies who get in the way but not seeking them out.

Couple more coins, a few arrows. At one point a flying eyeball flies down and tries to hit her, but it dies pretty easy and drops a small glass lens.

"Stars fall all over the world at night," Eric says when she opens the door. "They can be used for all sorts of useful things. If you gather 3 fallen stars, they can be combined to create an item that will increase your magic capacity."

Oooh, that sounds fun, especially if it also boosts her pre-existing magic in addition to her blasting staff. On the other hand, she's pretty hungry from all that mining. "How long does night last?"