Grand Motherload

Motherload came out in 2004 and I still think about it. You pilot a little drill rig into the earth, fill your cargo hold with ore, fly back to the surface, sell it, buy better equipment, and go deeper. That is the whole game. It is perfect.

This is my version, running right here. Same loop, my own world, no install.

The layers

The world is 40 tiles wide and 200 tiles deep, divided into eight depth bands. Each layer has its own palette, its own ore distribution, and a couple have nasty surprises waiting for you.

Layer	Depth	Notes
Topsoil	0–15m	Loose dirt and roots. Coal and copper.
Bedrock	15–35m	Bauxite, iron, the first silver.
Permafrost	35–55m	Frozen solid. Requires the Heated Drill upgrade or you cannot break a single tile. Methane ice deposits hide here.
Fossil layer	55–80m	Ancient sediment. Amber with insects, trilobite fossils.
Deep crust	80–110m	Cinnabar, gold, and the first uranium veins.
Magma veins	110–145m	Glowing red rock. Without a Heat Shield, your hull drains continuously while you are inside.
Crystal caves	145–180m	Tanzanite, more diamonds. The walls glitter.
Mantle edge	180–200m	Painite and unobtanium. Even worse heat than the magma layer. Endgame only.

What is down there

Eighteen things to mine, give or take. Some are real, some are deliberately not. Where the real ones are concerned I played a little fast and loose with relative values, but the general ordering (copper before silver before gold before tanzanite before painite) is roughly how the world works.

Ore	Value	Found in	Notes
Coal	$5	Topsoil → bedrock	Cheap and common.
Copper	$12	Topsoil → bedrock	Starter cash.
Bauxite	$25	Bedrock	Aluminum ore.
Iron	$35	Bedrock → deep crust	Ubiquitous.
Pyrite	$60	Bedrock	Fool's gold. Looks valuable, isn't.
Silver	$90	Bedrock → deep crust
Methane ice	$180	Permafrost	Heated drill required.
Cinnabar	$140	Deep crust	Mercury ore. Crystal clusters.
Gold	$200	Deep crust	The real thing.
Amber	$350	Fossil layer	Insect trapped inside.
Trilobite	$600	Fossil layer	Half-billion-year-old arthropod.
Uranium	$800	Deep crust	Glows. Requires drill Lv 3.
Obsidian	$280	Magma veins	Volcanic glass.
Emerald	$900	Fossil → crystal
Ruby	$1,400	Deep crust → crystal
Tanzanite	$2,000	Crystal caves	Real, found only in Tanzania.
Diamond	$3,000	Crystal caves	Requires drill Lv 4.
Painite	$6,000	Mantle edge	Real, briefly the world's rarest gem.
Unobtanium	$12,000	Mantle edge	Not real. Sue me.

Dirt and stone are not in this table because you do not collect them. You drill them, they disappear, you move on. The shop has six upgrades: drill, fuel, hull, cargo, plus a one-time Heated Drill purchase (gates the permafrost) and a two-tier Heat Shield (lets you survive the magma and mantle layers).

One piece of code I like

The world generates once at startup. Every tile rolls against a list of candidate ores filtered by depth, with rarer ores getting a slowly-increasing edge the deeper you go. The trick is walking the candidate list from rarest to most common, so diamond gets first dibs on the random number and common dirt only gets picked when nothing rarer has claimed the roll.

function pickOre(depth) {
  var candidates = [];
  for (var i = 0; i < ORE_KEYS.length; i++) {
    var o = ORES[ORE_KEYS[i]];
    if (depth >= o.minDepth) candidates.push(ORE_KEYS[i]);
  }
  var r = Math.random();
  // Deeper = rarer ores more likely. Walk from rarest to common.
  var cumul = 0;
  for (var j = candidates.length - 1; j >= 0; j--) {
    var ore = ORES[candidates[j]];
    var adjustedChance = ore.chance * (1 + depth * 0.003);
    cumul += adjustedChance;
    if (r < cumul / (cumul + 1)) {
      return { type: candidates[j], hp: ore.hp };
    }
  }
  if (Math.random() < 0.12) return null; // air pocket
  return { type: 'dirt', hp: ORES.dirt.hp };
}

Two things going on here. The cumul / (cumul + 1) bit is a soft normalization: it keeps the running probability bounded between 0 and 1 without needing to know the total ahead of time, which is handy because the candidate list changes with depth. And the depth multiplier (1 + depth * 0.003) is small but compounds. By 150 metres down, rare ores are getting a 45% bonus on every tile roll, which is why the crystal caves feel like a payday after the long climb to get there.