I adore the concept of this game! You know how you're playing Minecraft and you accidentally mine into a lava pit that burns you alive? Well, basically you've nailed the feeling of that in a game. It is cool to anchor the concept around the gameplay, which feels very arcadelike and fast-paced. I think you've done two things that really add depth: firstly, like Dig Dug, the pathing that you make when mining can trigger new streams of lava. Secondly, the lava is constant and follows the player through the trail they've made. Both of these really keep the player on their toes.
For constructive feedback, hmm - think about how the arcade design of the game could keep the player wanting to replay the game. Player incentive is a tricky thing. Maybe an unpredictable element or secondary threat, like the monsters in Dig Dug, are one way to add another gameplay layer. Or maybe it's just as simple as adding different types of gems that add different value to the score: this way, players are collecting gems, but trying to keep their eye out for the big one as they rush through their mine. I hope you keep on finding fun ideas like this - I enjoyed smashing and collecting gems!
My high score was 378, by the way!
Thanks for checking out SYMMACHUS and I hope you had a fun time making Mine Rush for the jam!